Apparatus and method for driving rotary machine

ABSTRACT

A motor driving apparatus has a loss-of-synchronism monitoring circuit that monitors the rotation of a rotary machine such as a brushless DC motor to detect a sign of transition to a state of loss of synchronism. When the sign is detected, an energization control circuit temporarily stops driving of the rotary machine to bring it into a free running state, and thereafter carries out control so as to resume driving of the rotary machine. Further, the motor driving apparatus has an inverter and a drive control circuit that controls switching operation of the inverter based on rotation of the rotary machine.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on an incorporates herein by referenceJapanese patent applications No. 2006-323947 filed on Nov. 30, 2006, No.2006-329430 filed on Dec. 6, 2006, No. 2007-25840 filed on Feb. 5, 2007,No. 2007-25841 filed on Feb. 5, 2007, No. 2007-25842 filed on Feb. 5,2007, No. 2007-40958 filed on Feb. 21, 2007, and 2007-232989 filed onSep. 7, 2007.

FIELD OF THE INVENTION

The present invention relates to an apparatus and a method for drivingrotary electric machines such as a brushless DC motor, wherein the rotorposition of the rotary machine is estimated to determine theenergization time point for driving the rotary machine.

BACKGROUND OF THE INVENTION

Some of conventional driving apparatuses adopt a position sensorlessmethod so designed as to estimate the rotor position of a brushless DCmotor and thereby obtain the commutation time point of the motor anddrive it. If a trouble occurs in such a driving apparatus or loadfluctuation occurs, it can be brought into a state of loss ofsynchronism in which it cannot drive the motor as intended any more.

JP-A-2004-104935 discloses a technology for, when it is detected that amotor has been brought into a state of loss of synchronism and hasstopped, resuming drive control on the motor. However, according to thistechnique, in case of a motor or the like for driving an electricvehicle, it is inappropriate to stop the rotation of the motor while thevehicle is traveling even though it has been brought into a state ofloss of synchronism. The rotation of the motor must be maintained asmuch as possible. In this technique, after it is detected that a motorhas completely lost synchronism, the loss of synchronism is coped with.

JP 4-317587A, U.S. Pat. No. 5,432,414 (JP 5-284781A) and JP 7-327390Adisclose technologies for starting the motor by varying a frequency ofexcitation (energization) of the motor. Those technologies are proposed,because a motor is temporarily rotated in a reverse direction or torqueproduced in a motor is too large, and this causes over-speed and loss ofsynchronism, resulting in a lengthened starting time in the conventionalapparatus. However, the proposed circuit for varying an excitationfrequency is complicated, and this inevitably increases the size of thecircuit. For example, when an excitation frequency is varied by digitalprocessing, the number of bits of a counter for counting cyclescorresponding to a frequency is increased.

JP 11-18478A disclose a technology to detect a time point at which anelectrical angle of a motor becomes equal to a predetermined electricalangle based on an induced voltage developed as a terminal voltage of themotor. According to this technology, limitation is imposed on apermitted period for which detection of a time when the predeterminedelectrical angle occurs is permitted. However, a detected value of therotational speed of a motor transitions to too high a value or too low avalue and is fixed there. In these cases, it is difficult to control therotating state of the motor as desired. When it transitions to too higha value or too low a value, a time when a predetermined electrical angleoccurs does not fall within the permitted period. There are cases where,for example, power supply voltage or the load on a motor abruptlyfluctuates and this causes the rotational speed of the motor to abruptlyfluctuate. Also, in these cases, a time when a predetermined electricalangle occurs may temporarily fall outside the permitted period. For thisreason, if, when a time when a predetermined electrical angle occursdoes not fall within a permitted period, the rotating state isdetermined to be abnormal. There is a possibility that both a state(loss of synchronism state) in which it is difficult to control therotating state as desired and a temporary rotational fluctuation statecaused by load variation or the like are determined to be abnormal. Itis thus difficult, for example, to continuously control a rotary machineif only load variation occurs.

US 2005/0258788 (JP 2005-333689A) discloses determination of anelectrical angle of a motor by detecting induced voltages, that is,terminal voltages. When a three-phase motor is started, all switchingelements of an inverter are OFF, and thus each phase of the three-phasemotor is in a high-impedance state. For this reason, a situation inwhich a neutral point voltage is equal to the potential of each phase ofthe three-phase motor can occur. If noise is mixed when the inducedvoltage is detected in this state, the neutral point voltage and thevoltage of each phase frequently cross each other. Eventually, thezero-crossing time is frequently erroneously detected. For this reason,for example, a system required to operate an inverter based on adetection signal with respect to zero-crossing time point fromimmediately after start of a three-phase motor cannot appropriately meetthis requirement.

Further, in US 2005/0258788, the time required for the rotor to rotateby a predetermined interval of electrical angle is determined from timeintervals between occurrences of time point with which the abovezero-crossing occurs. Time point with which the time required passesafter an occurrence of zero-crossing time point is taken as specifiedtime point with which an angle that provides a basis for switchingoperation occurs. When a specified time point is set by the above methodwhen the three-phase motor is started, the specified time point is setby shortening the predetermined interval of electrical angle used in theabove computation of the time required. If this time point is calculatedin the initial stage of startup as under normal conditions, this timepoint is unexceptionally delayed from a time point with which areference angle occurs. In this case, the specified time point is set bydetermining a time required from an occurrence of zero-crossing timepoint to when a reference angle occurs based on a time interval betweenoccurrences of the zero-crossing time point. The inventors found that,to make this setting with accuracy, the rotational speed of the motormust be stable. For this reason, the time point with which the referenceangle occurs cannot be set with accuracy not only when the motor isstarted but also generally when the rotational speed largely fluctuates.This can lead to degraded controllability of the motor.

JP 2642357B1 discloses an example of a conventional control apparatusfor multi-phase rotary machines. In another technique for controlling arotary machine (three-phase brushless motor), a 120°-energization methodillustrated in FIG. 50 is proposed. In this figure, (a) illustrates thetransition of terminal voltages Vu, Vv, Vw; (b) illustrates thetransition of comparison signals PU, PV PW as a result of comparisons ofthe terminal voltages Vu, Vv, Vw indicated by solid lines in (a) with areference voltage Vref; (c) illustrates the transitions of a one-bitcombined signal PS obtained by logically combining the comparisonsignals PU, PV, PW; and (d) illustrates the transition of a detectionsignal Qs obtained by shaping the waveform of the combined signal PS.With time point (zero-crossing time point) with which the terminalvoltages Vu, Vv, Vw indicated by (a) agree with the reference voltageVref, the output of the comparison signals PU, PV, PW is inverted. Inreality, however, the output of the comparison signals PU, PV, PW isalso inverted when the operation of the switching elements of aninverter (power conversion circuit) connected with the brushless motoris changed. This inversion is caused by the passage of a current throughdiodes connected in parallel with the switching elements. For thisreason, the rising edges and the falling edges of the combined signal PSobtained by logically synthesizing the comparison signals PU, PV, PWcoincide with not only zero-crossing time point. Some of them coincidewith time point with which a current is supplied though the diodes.Meanwhile, all the rising edges and the falling edges of the detectionsignal Qs obtained as a result of waveform shaping coincide withzero-crossing time point.

The electrical angle of the brushless motor is uniquely determined byzero-crossing time point. For this reason, the following can beimplemented by changing the operating state of switching elements at thetime (specified time point) when a time required for a motor to rotateby a predetermined angular interval (e.g., 30°) from the zero-crossingtime has passed. The brushless motor can be controlled by a120°-energization method. More specifically, a time-series pattern withrespect to the operation of switching elements is predetermined.Therefore, control by the 120°-energization method can be achieved byoperating the switching elements according to the above pattern eachtime the specified time point occurs.

Since the detection signal Qs is a one-bit signal, it is impossible todiscriminate one zero-crossing time from another in the three-phasebrushless motor according to the signal. For this reason, if therotating state of a brushless motor becomes abnormal or noise is mixedin a terminal voltage Vu, Vv, Vw or the like, there is a possibilitythat the controllability of the brushless motor is significantlydegraded. More specific description will be given. Even if the brushlessmotor is rotated in reverse, for example, it is difficult to detect thisreverse rotation from the detection signal Qs. Therefore, there is apossibility that change of the operation of the switching elements whena time required from a rising edge or a falling edge of the detectionsignal Qs has passed (specified time point) is continued as under normalconditions. In this case, the brushless motor cannot be appropriatelycontrolled.

There is known a technique for carrying out the following for thepurpose of controlling the output of the brushless motor, controllingand limiting a current supplied to the brushless motor, or for otherlike purposes. During a permitted period for the on operation ofswitching elements, defined based on the above specified time point, PWMmodulation processing is carried out to repeatedly turn on and off theswitching elements. In this case, however, a problem arises. In PWMmodulation processing, switching elements are frequently switched fromON state to OFF state, and a current is thereby frequently passedthrough diodes. Eventually, the comparison signals PU, PV, PW and thecombined signal PS are frequently inverted. At this time, it isdifficult to generate the detection signal Qs as an appropriate signalsynchronized with zero-crossing time point. Therefore, it is difficultto appropriately set a specified time point.

SUMMARY OF THE INVENTION

It is therefore a first object of the present invention to provide arotary machine driving apparatus and method, wherein drive control canbe restored without stopping the operation of a rotary machine driven bya sensorless method before the rotary machine is completely brought intoa state of loss of synchronism. For attaining the first object, a stateof rotation of the rotary machine is monitored to detect a sign of therotary machine transitioning to a state of loss of synchronism, anddriving of the rotary machine is temporarily stopped to bring the rotarymachine into a free running state when the sign is detected. Thereafter,normal control for driving the rotary machine is resumed.

It is a second object of the present invention to provide a rotarymachine driving apparatus and method, wherein a rotary machine can bestarted in a short time by a simple construction. For attaining thesecond object, forced commutation of a rotary machine is carried out,and a current supplied to a winding of the rotary machine is limited toan upper limit level set higher than a level at which a current flowswhen the rotary machine is in a normal rotating state, when the forcedcommutation is carried out.

It is a third object of the present invention to provide a rotarymachine driving apparatus that is capable of more appropriatelydetecting a rotating state of a rotary machine based on an inducedvoltage of the motor. For attaining the third object, a permitted periodfor which detection of a predetermined electrical angle based on adetected value of a terminal voltage of a rotary machine is permitted,and a rotating state of the rotary machine is determined to be abnormalwhen the number of times the predetermined electrical angle continuouslyoccurs either ahead of or behind the permitted period becomes equal toor higher than a threshold value.

It is a fourth object of the present invention to provide a rotarymachine driving apparatus that avoids erroneous detection of azero-crossing time point at which a neutral point voltage becomes equalto a reference voltage. For attaining the fourth object, a terminalvoltage of a rotary machine is compared with a reference voltage withrespect to magnitude to detect a zero-crossing time point when thereference voltage, which is either a neutral point voltage of the rotarymachine or an equivalent thereof, and an induced voltage of the rotarymachine agree with each other. A switching element for supplying currentto the rotary machine is operated based on the zero-crossing time point.At least one of a value of the terminal voltage to be compared when arotational speed of the rotary machine is substantially zero and a valueof the reference voltage is offset-corrected so as to differentiate thevalues of the terminal voltage and the reference voltage.

It is a fifth object of the present invention to provide a rotarymachine driving apparatus, wherein information pertaining to theelectrical angle of a rotary machine can be acquired with higheraccuracy based on a result of comparison of an induced voltage of therotary machine with a reference voltage. For attaining the fifth object,a terminal voltage of each phase of a rotary machine is compared with areference voltage, and information pertaining to an electrical angle ofthe rotary machine is acquired based on a result of comparison when azero-crossing time point occurs in a present operating state ofswitching elements and an actual result of comparison with respect toeach phase. It may be determined whether an abnormality is present in arotating state of the rotary machine based on a detected value of aninduced voltage of the rotary machine, and all the phases of the rotarymachine may be conducted to either the positive pole or the negativepole of a power supply and thereby forcibly stopping the rotation of therotary machine when an abnormality is detected.

It is a sixth object of the present invention to provide a rotarymachine driving apparatus, wherein when switching elements of a powerconversion circuit are operated to control a rotary machine, moreappropriately determining time point with which a reference angle occursbased on a zero-crossing time point with which an induced voltage of therotary machine becomes equal to a reference voltage regardless offluctuation in rotational speed. For attaining the sixth object,information pertaining to a change in a rotational speed of a rotarymachine is extracted from a result of detection of the zero-crossingtime point, and a specified time point for controlling the rotarymachine is variably set based on the information pertaining to thechange in the rotational speed. The information is acceleration. Anamount of energization to the rotary machine is limited according to theacceleration. The rotary machine is supplied with a current from onepart of phases to another part of phases thereof before the rotarymachine is started so that a rotation angle of the rotary machine isfixed at a predetermined angle. At least one of the one part of phasesand the another part of phases includes a plurality of phases.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a circuit diagram illustrating a rotary machine drivingapparatus in a first embodiment of the invention;

FIG. 2 is a flowchart illustrating processing carried out by a drivecontrol circuit and a loss-of-synchronism monitoring circuit;

FIG. 3 is a signal diagram illustrating output voltage waveforms of aninverter unit observed when a motor is rotating;

FIG. 4 is a signal diagram illustrating a second embodiment of theinvention;

FIG. 5 is a signal diagram explaining fluctuation in a switching signalwhen switching is made earlier;

FIG. 6 is a signal diagram explaining fluctuation in a switching signalwhen switching is made irregularly;

FIG. 7 is a circuit diagram illustrating a third embodiment of theinvention; corresponding to FIG. 1.

FIG. 8 is a signal diagram corresponding to FIG. 3;

FIG. 9 is a circuit diagram illustrating a fourth embodiment of theinvention partly corresponding to FIG. 1;

FIG. 10 is an operation diagram illustrating a state in which a currentfluctuates before a motor loses synchronism;

FIG. 11 is a circuit diagram illustrating a rotary machine drivingapparatus in a fifth embodiment of the invention;

FIG. 12 is a signal diagram illustrating voltages of respective phasesand position signals of a rotor observed when a motor is rotating in anormal condition;

FIG. 13 is a circuit diagram illustrating a gate drive circuit;

FIG. 14 is a signal diagram illustrating a waveform developed when agate drive circuit limits a starting current;

FIG. 15 is a signal diagram illustrating voltages of the respectivephases and a motor current observed when a current supplied when a motoris actually started is limited to 2 A;

FIG. 16 is an explanatory diagram illustrating change in starting timeobserved when a current is not limited and limited to various limitlevels when a motor is started;

FIG. 17 is a flowchart illustrating a part of processing carried out bythe drive control circuit when the motor is started;

FIG. 18 is a circuit diagram illustrating a rotary machine drivingapparatus for a brushless motor in a sixth embodiment;

FIG. 19 is a signal diagram illustrating a mode for carrying out120°-energization control;

FIG. 20 is a flowchart illustrating processing for setting counters for120°-energization control;

FIG. 21 is a flowchart illustrating a mode for operating switchingelements;

FIG. 22 is a flowchart illustrating processing for correcting a countspeed of counters;

FIG. 23 is a characteristic diagram illustrating a relation between avoltage variation and a count speed correction coefficient;

FIG. 24 is a flowchart illustrating processing for determination of aloss of synchronism state;

FIG. 25 is a flowchart illustrating processing for the determination ofa loss of synchronism state;

FIG. 26A is a flowchart illustrating processing for correcting the countspeed of counters in a seventh embodiment;

FIG. 26B is a characteristic diagram illustrating a relation between anacceleration and a count speed correction coefficient;

FIG. 27A is a signal diagrams illustrating a method for setting amaximum advance counter in an eighth embodiment;

FIG. 27B is a signal diagrams illustrating a count operation of amaximum advance counter;

FIG. 28 is a flowchart illustrating determination of a loss ofsynchronism state;

FIG. 29 is a table illustrating a relation of count speed correctioncoefficient relative to a voltage and a voltage variation in onemodification;

FIG. 30 is a table illustrating a relation of count speed correctioncoefficient relative to a voltage variation and a motor temperature inanother modification;

FIG. 31 is a circuit diagram illustrating a rotary machine drivingapparatus in a ninth embodiment;

FIG. 32 is a signal diagram illustrating a mode for 120°-energizationcontrol;

FIG. 33 is a signal diagram illustrating a mode for detecting reverserotation;

FIG. 34 is an operation diagram illustrating a relation between forwardrotation and reverse rotation;

FIG. 35 is a flowchart illustrating restart processing at the time ofreverse rotation;

FIG. 36A to 36E are signal diagrams illustrating transition of referencevoltage and terminal voltages that occurs when a brushless motor whoserotation has been stopped is started;

FIG. 37 is a circuit diagram illustrating a comparator in a tenthembodiment;

FIG. 38 is a circuit diagram illustrating a rotary machine drivingapparatus in an eleventh embodiment;

FIG. 39 is a signal diagram illustrating a mode for 120°-energizationcontrol;

FIG. 40 is a flowchart illustrating processing for operating switchingelements;

FIG. 41 is a flowchart illustrating processing for changing theoperation of the switching elements;

FIG. 42 is a flowchart illustrating processing in PWM control;

FIG. 43 is a signal diagram illustrating a mode for PWM control;

FIG. 44 is a signal diagram illustrating a mode of reverse rotation;

FIG. 45 is an operation diagram illustrating a relation between forwardrotation and reverse rotation;

FIG. 46 is a flowchart illustrating processing for restarting abrushless motor in a twelfth embodiment;

FIG. 47 is a signal diagram illustrating a principle of wiredisconnection in a thirteenth embodiment;

FIG. 48 is a flowchart illustrating processing for detecting wiredisconnection;

FIG. 49 is a circuit diagram illustrating a rotary machine drivingapparatus in a fourteenth embodiment;

FIG. 50 is a signal diagram illustrating a mode of conventional120°-energization control;

FIG. 51 is a circuit diagram illustrating a rotary machine drivingapparatus in a fifteenth embodiment;

FIG. 52 is a signal diagram illustrating a mode of switching control;

FIG. 53 is a signal diagram illustrating a mode of switching control;

FIG. 54 is a flowchart illustrating processing for setting variouscounters;

FIG. 55 is a flowchart illustrating processing for switching onswitching elements;

FIGS. 56A and 56B are signal diagrams illustrating deviation in inducedvoltage between normal and acceleration time;

FIGS. 57A and 57B are graphs illustrating results of experiments ondetection error in the angle of a rotor at acceleration;

FIGS. 58A and 58B are a flowchart and a data table illustratingprocessing for setting a specified time point;

FIG. 59 is a signal diagram illustrating result of simulation on the wayrotational speed is increased when a motor is started with correction;

FIG. 60 is a signal diagram illustrating result of simulation on the wayrotational speed is increased when a motor is started withoutcorrection;

FIGS. 61A and 61B are a flowchart and a data table illustratingprocessing for setting a specified time point in a sixteenth embodiment;

FIG. 62 is a flowchart illustrating processing for estimating azero-crossing time point in a seventeenth embodiment;

FIG. 63 is a flowchart illustrating processing for limiting a current inan eighteenth embodiment;

FIGS. 64A and 64B are circuit diagrams illustrating positioningprocessing carried out before a brushless motor is started in anineteenth embodiment;

FIGS. 65A and 65B are signal diagrams illustrating a time it takes forthe angle of a rotor to settle by the positioning processing;

FIG. 66 is a graph illustrating a relation between an angle at which arotor is fixed by positioning processing and a starting time;

FIG. 67 is a signal diagram illustrating a relation between an angle atwhich a rotor is fixed by positioning processing and torque generatedwhen startup operation is started;

FIG. 68 is a flowchart illustrating positioning processing;

FIG. 69 is a flowchart illustrating positioning processing in atwentieth embodiment;

FIG. 70 is a flowchart illustrating positioning processing in atwenty-first embodiment;

FIG. 71 is a flowchart illustrating positioning processing in atwenty-second embodiment;

FIG. 72 is a flowchart illustrating processing for limiting an amount ofenergization in positioning processing in a twenty-third embodiment;

FIG. 73 is a flowchart illustrating processing for starting startup of abrushless motor in a twenty-fourth embodiment; and

FIG. 74 is a signal diagram illustrating transition of a voltage of abattery at startup.

DETAILED DESCRIPTION OF THE EMBODIMENTS First Embodiment

Referring to FIG. 1, a rotary machine driving apparatus 1 is suppliedwith driving power voltage VB from a battery (not shown) for vehicledriving power. A brushless DC motor 2, which is a rotary machine, isdriven through an inverter unit 3. The inverter unit 3 is constructed asa power conversion circuit by, for example, connecting six N-channelpower MOSFETs 3 a to 3 f in a three-phase bridge configuration. Theoutput terminals of the respective phases of the inverter unit 3 arerespectively connected to the stator coils (windings) 2U, 2V, 2W of therespective phases of the motor 2. The arrows facing downward in thefigure indicate ground.

The inverter unit 3 is controlled by a drive control circuit (drivecontrolling means) 4 constructed of a microcomputer or a logic circuit.Driving signals are outputted to the gates of the FETs 3 a to 3 fthrough gate drive circuits 5 a to 5 f. Comparators 6U, 6V, 6W comparethe output voltage of each phase of the inverter unit 3 with virtualneutral point potential. Then, they output comparison signals PU, PV, PWto the drive control circuit 4 and a loss-of-synchronism monitoringcircuit (loss-of-synchronism predicting means) 7. The (+) terminals ofthe comparators 6U, 6V, 6W are respectively connected to the outputterminals OUTu, OUTv, OUTw of the respective phases of the inverter unit3. The (−) terminals of the same are connected with a reference voltagesource 8 equivalent to the virtual neutral point potential (or VB/2) incommon.

The drive control circuit 4 generates a commutation pattern signal forthe inverter unit 3 based on the comparison signals PU, PV, PW andoutputs it to the gate of each FET 3 through the corresponding gatedrive circuit 5. Similarly with the drive control circuit 4, theloss-of-synchronism monitoring circuit 7 is constructed of amicrocomputer or a logic circuit. It detects a sign (possibility) of themotor 2 transitioning to a state of loss of synchronism based on theabove comparison signals PU, PV, PW. When the sign is detected, itoutputs a drive stop signal to the drive control circuit 4 only for apredetermined time. As long as the drive stop signal is being outputted,the drive control circuit 4 stops drive control of the inverter unit 3to keep the motor 2 in a free running state.

The drive control circuit 4 and the loss-of-synchronism monitoringcircuit 7 carries out processing of FIG. 2. When power to the drivingapparatus 1 is turned on, the drive control circuit 4 excites thewindings 2U, 2V, 2W of the motor 2 by direct current to position itsrotor (step 1: S1). Thereafter, the windings 2U, 2V, 2W are energizedaccording to a predetermined commutation pattern, and thus the motor 2is started by forced commutation (S2).

When the number of revolutions of the motor 2 is increased to somedegree after it is started, induced voltage developed in the windings2U, 2V, 2W can be observed. Consequently, the drive control circuit 4changes the driving scheme for the motor 2 to sensorless mode (S3). Thatis, a commutation pattern signal for the inverter unit 3 is generatedbased on the comparison signals PU, PV PW, and gate signals UH to WL areoutputted to the gates of the individual FETs 3 a to 3 f. Thezero-crossing time point of induced voltage has a phase delay of anelectrical angle of 30° from appropriate energization time point.Therefore, the drive control circuit 4 adjusts this phase delay when itgenerates a commutation pattern signal.

While the motor 2 is being driven in the sensorless mode, theloss-of-synchronism monitoring circuit 7 acquires data for predictingloss of synchronism (54). Based on this data, it checks whether or notthere is a sign (possibility) of loss of synchronism in the drivingstate of the motor 2 (S5). When it is determined that there is no signof loss of synchronism (“NO”), the processing proceeds to S7.

At S7, the drive control circuit 4 checks whether or not the motor 2 isrotating at this point of time based on the comparison signals PU, PV,PW. When the motor is rotating (“YES”), the processing returns to S3,and sensorless mode is continued. When the motor 2 is at a stop (“NO”),the processing returns to S1, and the motor 2 is restarted by carryingout the processing of initial positioning and then forced commutation.

The prediction and detection of loss of synchronism at S4 and S5 arecarried out as described below. FIG. 3 illustrates the waveforms of theoutput voltages of the inverter unit 3 observed when the motor 2 isrotating. When a three-phase motor is driven, its voltage waveforms areas follows. Two phases energized between high side and low side arebrought to high level and low level, and the remaining one phase notenergized is in a high impedance state. During this period, inducedvoltages Vu, Vv, Vw develop in the windings 2U, 2V and shows transientvoltage change between high level and low level. In FIG. 3, the inducedvoltages Vu, Vv, Vw are depicted as though it is linearly increased ordecreased during the above period. In reality, however, the inducedvoltages sinusoidally change.

The intervals (between different phases) at which the zero-crossingpoint of induced voltage is produced for a non-energization period ineach phase are a period T60 equivalent to an electrical angle of 60°.When a commutation pattern is changed, as illustrated in FIG. 3, (a) to(c), a current flows back through the flywheel diodes of the FETs 3 a to3 f for an instantaneous period, and a “zero-crossing” point isproduced. Therefore, the above period is reflected in the comparisonsignals PU to PW outputted by the comparators 6U to 6W. However, thisperiod is disregarded by waveform processing in the drive controlcircuit 4 and the loss-of-synchronism monitoring circuit 7. As a result,position signals PU′, PV′, PW′ are generated as illustrated in FIG. 3,(d) to (f).

The loss-of-synchronism monitoring circuit 7 detects the zero-crossinginterval period T60 between phases based on the position signals PU′,PV′, PW′. Then, it checks whether or not the period T60 is equal to thetime corresponding to the normal number of revolutions of the motor 2.For example, when the normal number of revolutions of the motor 2 is10,000 rpm at a rated speed and the number of poles of the motor 2 is N,⅙ of the rotation period per unit time is (2/N)ms. Therefore, when thezero-crossing interval period T60 becomes longer than (2/N)ms by apredetermined time, the loss-of-synchronism monitoring circuit 7determines that the motor 2 is likely to transition to a state of lossof synchronism (“YES” at S5). Then, it outputs a drive stop signal tothe drive control circuit 4.

Then, the drive control circuit 4 stops drive control on the motor 2 forthe period for which the drive stop signal is being outputted. Thus, itkeeps the motor 2 in a free running state (free running control, S6).The time for which the motor 2 is kept in a free running state at thistime is, for example, several hundreds of μs to several ms or so. Afterthe motor 2 is kept in a free running state only for the predeterminedtime, the drive control circuit 4 proceeds to S7. When the rotation ofthe motor 2 has not been stopped (“YES”), it continues drive control inthe sensorless mode.

According to the first embodiment, the following is implemented. Theloss-of-synchronism monitoring circuit 7 of the rotary machine drivingapparatus 1 monitors the state of rotation of the brushless DC motor 2to detect a sign of the motor 2 transitioning to a state of loss ofsynchronism. When the sign is detected, the drive control circuit 4temporarily stops driving of the motor 2 and brings it into a freerunning state. Thereafter, it carries out control so as to resumedriving of the motor 2. Therefore, it is possible to prevent the motorfrom stopping as a result of the motor having completely lostsynchronism, and to continue rotational driving of the motor.

Specifically, the loss-of-synchronism monitoring circuit 7 detects thespeed of the motor 2 and compares the detected speed with the normalspeed of the motor 2. When the difference between them becomes equal toor higher than a predetermined value, it detects a sign of transition toa state of loss of synchronism. When the motor 2 is likely to losesynchronism, the speed of the motor 2 rapidly fluctuates. Theloss-of-synchronism monitoring circuit 7 detects a period T60 equivalentto an electrical angle of 600 based on the zero-crossing time point ofthe induced voltage of the motor 2. Then, it compares the length of thedetected period T60 with a period equivalent to an electrical angle of60° at the normal speed. Therefore, a sign of transition to a state ofloss of synchronism can be easily detected.

Second Embodiment

In a second embodiment illustrated in FIGS. 4 to 6, a differentdetecting scheme is used to predict loss of synchronism, which iscarried out at S4 and S5 in FIG. 2. The loss-of-synchronism monitoringcircuit 7 in the second embodiment carries out logic combination thereinbased on the position signals PU′, PV′, PW′ and generates a switchingsignal Ssw as illustrated in FIG. 4, (g).

The switching signal changes to high level during a period for whichposition signals PU, PV′, PW′ of any two phases are brought to highlevel. It thereby repeatedly changes to high and low levels for a periodequivalent to an electrical angle of 60°. When the motor 2 is rotatingat the normal speed, the output voltage of each phase of the inverterunit 3 repeats a predetermined pattern. Therefore, the switching signalSsw is a rectangular wave signal with a duty cycle of 50%. When apattern different from the predetermined pattern is produced, there is ahigh possibility of transition to loss of synchronism. Therefore, theloss-of-synchronism monitoring circuit 7 monitors the output state ofthe switching signal to predict loss of synchronism.

The waveform of the switching signal illustrated in FIG. 5 indicates acase where the commutation time point of the motor 2 becomes earlierthan the normal speed. This is an abnormal state in which the period ofthe switching signal is rapidly shortened. Conversely, if thecommutation time point becomes slower, the period of the switchingsignal is lengthened. The waveform of the switching signal illustratedin FIG. 6 indicates a case where the commutation time point of the motor2 is not changed as expected or regularly. This is also an abnormalstate in which the period of the switching signal is temporarilyshortened. When any of these states are detected over a predeterminedtime, that is considered as a sign of the motor 2 losing synchronism,“YES” determination is made at S5.

According to the second embodiment, the loss-of-synchronism monitoringcircuit 7 carries out the following processing. When a period for whicha pattern of development of the output voltage of each phase of theinverter unit 3 disagrees with a predetermined pattern becomes equal toor larger than a predetermined value, it detects a sign of transition toa state of loss of synchronism. Therefore, the sign can be reliablydetected.

Third Embodiment

In a third embodiment illustrated in FIG. 7 and FIG. 8, aloss-of-synchronism monitoring circuit (loss-of-synchronism predictingmeans) 7 monitors a pattern of development of induced voltage of eachphase. For this purpose, three comparators 13 are provided for eachphase.

Similarly with the comparators 6U, 6V, 6W in the first embodiment,comparators 13UM, 13VM, 13VM compare the output voltages of the inverterunit 3 with the virtual neutral point potential of a reference voltagesource 8M. Comparators 13UH, 13VH, 13WH compare the above outputvoltages with the high-side threshold value of a reference voltagesource 8H set higher than the potential of the reference voltage source8M. Comparators 13UL, 13VL, 13WL compare the above output voltages withthe low-side threshold value of a reference voltage source 8L set lowerthan the potential of the reference voltage source 8M.

Though not shown in FIG. 7, the comparison signals PU, PV, PW outputtedby the comparators 13UM, 13VM, 13VM are supplied to the drive controlcircuit 4 as in the first embodiment. In FIG. 7, the flywheel diodes ofthe FETs 3 a to 3 f are not illustrated, and a gate drive circuit 5 (5 ato 5 f) is illustrated in a block form.

With respect to operation common to all the phases, reference numeralswill not be suffixed with “U, V, or W” in the following description. Theloss-of-synchronism monitoring circuit 7 monitors the energizationpattern for each phase based on position signals PH′, PM′, PL′ obtainedfrom comparison signals PH, PM, PL outputted by the comparators 13H,13M, 13L. At this time, it discriminates the energization pattern intothree levels: high level SH, intermediate level (high impedance) SM, andlow level SL. FIG. 8, (d), (e), (f) illustrate position signals PUH′,PUM′, PUL′ of U-phase.

More specifically, high level SH and low level SL are respectivelydetermined by SH=PH′ and SL=/PL′. (“/” represents negation.)Intermediate level SM is determined as follows.SM=(/PH′·PM′)+(/PM′·PL′)

Since intermediate level SM can be determined, the following can beimplemented. When the rotation of the motor 2 is normal (insteady-state), the loss-of-synchronism monitoring circuit 7 canrecognize that the energization pattern in each of the U, V, andW-phases transitions from state 1 to state 6, tabled below, every 60° ofelectrical angle. Here, “M” represents high impedance.

State 1 2 3 4 5 6 U L L M H H M V H M L L M H W M H H M L L

Consequently, the loss-of-synchronism monitoring circuit 7 monitorswhether or not the above cycle of from state 1 to state 6 is repeated ina correct (normal) pattern. If there is deviation from the correctpattern, it determines that there is a sign of loss of synchronism.

According to the third embodiment, the loss-of-synchronism monitoringcircuit 7 carries out the following processing. In detecting a patternof development of output voltage of each phase for the motor 2, itdiscriminates the output voltage into three levels: high level, lowlevel, and non-energization level (intermediate level). Therefore, thestate of rotation of the motor can be more definitely monitored.

In the third embodiment, intermediate level SM may be further dividedinto two levels to subdivide a pattern of output voltage.SMH=/PH′·PM′SML=/PM′·PL′

Further, the comparators 13UM, 13VM, 13VM may be removed, anddetermination may be carried out bySM=/PH′·PL′.

With respect to states 1 to 6, the following measure may be taken. Onlya period “M” for which high impedance is achieved is selectivelydetected, and it is monitored whether or not the developmental patternfor the period “M” is normally cycled.

Fourth Embodiment

In a fourth embodiment illustrated in FIGS. 9 and 10, a rotary machinedriving apparatus 1 is so constructed that a loss-of-synchronismmonitoring circuit (loss-of-synchronism predicting means) 7 detects acurrent supplied to a motor 2, and predicts loss of synchronism based onthe state of fluctuation in the current. The drain and gate of FET 3 aof the inverter unit 3 are respectively connected with the drain andgate of a current sensing N-channel power MOSFET 23. They aresimultaneously turned on/off by a common gate signal. The FETs 3 a, 23are so set that, when they are turned on, the ratio of currentsrespectively passing therethrough is 100:1 to 5000:1 or so.

The source of the FET 23 is connected to a ground wire through a diode24, the collector-emitter of an NPN transistor 25, and a resistor 26,and is further connected to the (+) terminal of an operational amplifier27. The (−) terminal of the operational amplifier 27 is connected to thesource of the FET 3 a, and its output terminal is connected to the baseof the transistor 25. The emitter of the transistor 25 is connected tothe (+) terminal of a comparator 28, and the (−) terminal of thecomparator 28 is connected to a voltage source 29 for supplyingreference voltage for comparison. The comparator 28 is so constructedthat its output signal is inputted to the drive control circuit 4.

When the FETs 3 a, 23 are simultaneously turned on, drain currentscorresponding to their current ratio are respectively passed throughthem. In this case, their source voltages become equal to each other dueto the operation (imaginary shorting) of the operational amplifier 27.Even though the resistor 26 is connected to the current sensing FET 23,therefore, their current ratio is kept as specified.

The current supplied when the FET 23 is turned on flows to the resistor26 by way of the diode 24 and the transistor 25. The terminal voltage ofthe resistor 26 is compared with the reference voltage of a voltagesource 29 by the comparator 28. When the level of the former becomeshigher, the comparator 28 changes the output signal to high level.

As illustrated in FIG. 10, a current supplied to the motor 2 fluctuatesbefore it transitions to a state of loss of synchronism. However, thecurrent depicted in this figure is not a current detected by the FET 23but the total through a direct-current power supply line. When the motor2 is rotating in a normal (steady) state, the current hardly fluctuatesand is substantially constant. When some trouble occurs in the rotationof the motor 2 and its output torque largely fluctuates or on other likeoccasions, fluctuation in the current is also increased in conjunctiontherewith. Therefore, the loss-of-synchronism monitoring circuit 7predicts loss of synchronism by detecting current fluctuation (increase)at this time.

More specifically, when the comparator 28 changes the output signal tohigh level, the drive control circuit 4 is triggered by this levelchange and brings the motor 2 into a free running state. Theseprocessing correspond to the processing of S4 to S6 in FIG. 2.

According to the fourth embodiment, the loss-of-synchronism monitoringcircuit 7 detects a current supplied to the motor 2. When fluctuation inthe current becomes equal to or higher than a predetermined value, itdetects a sign of loss of synchronism. Therefore, loss of synchronismcan be reliably predicted.

In the first to fourth embodiments, loss of synchronism may be predictedby combining loss of synchronism predicting methods in variousembodiments and applying an OR condition. The embodiments are applicablenot only to those for driving the drive motor of an electric vehicle. Itcan be widely utilized in applications in which it is difficult to stopa brushless DC motor by loss of synchronism when the motor is driven bya sensorless method.

Fifth Embodiment

In a fifth embodiment illustrated in FIG. 11, a rotary machine drivingapparatus 1 is configured to drive a motor for driving, for example, amini disk (MD) or a hard disk drive (HDD). This rotary machine drivingapparatus 1 is similar to that of the first embodiment (FIG. 1), but hasno loss-of-synchronism monitoring circuit. However, a drive controlcircuit 4 includes an internal counter (not illustrated) to measure aninterval between the edges of the position signals PU′, PV′, PW′ tomeasure a zero-cross period T60 corresponding to electrical angle of 60°as illustrated in FIG. 12, (g). The zero-cross time point of the inducedvoltage has a phase delay of an electrical angle of 30° from anappropriate energization time point. Therefore, the drive controlcircuit 4 generates a commutation pattern by compensating for the phasedelay. The time interval corresponding to the electric angle of 30° maybe determined as T60/2. The waveforms of the output voltage of theinverter unit 3 observed when the motor 2 is rotating are illustrated inFIG. 12. When the three-phase motor 2 is driven, its voltage waveformsare similar to that of the first embodiment (FIG. 3).

High side gate drive circuits 5 a, 5 c, 5 f are constructed similarly toeach other. For instance, the gate drive circuit 5 a is constructed asillustrated in FIG. 13. The drain and gate of the FET 3 a thatconstructs the inverter unit 3 are respectively connected with the drainand gate of a current sensing N-channel power MOSFET 107. They aresimultaneously turned on and off by a common gate signal. The FETs 3 a,107 are so set that, when they are turned on, the ratio of currentsrespectively passing therethrough is, for example, 100:1 to 5000:1 orso.

Between the power supply line (VB) and a ground wire, there is connecteda series circuit of resistors 111 and 112 and an N-channel MOSFET 113.The common connection point of the resistors 111 and 112 is connectedwith the base of a PNP transistor 114, and the emitter of the transistor114 is connected to the power supply line. The collector of thetransistor 114 is connected to the gates of the FETs 107 and 3 a througha booster circuit section 115 and a diode 116.

Between the anode of the diode 116 and the source of the FET 107, twoZener diodes 117 and 118 are connected in series so that they are inopposite direction to each other. The booster circuit section 115 is forcarrying out a voltage boosting operation to obtain a gate voltagerequired to drive the high-side N-MOSFETs 3 a and 107. It is constructedof a conventional charge pump circuit constructed of a combination ofdiodes and capacitors.

The source of the FET 107 is connected to the ground wire through adiode 119, the collector-emitter of an NPN transistor 120, and aresistor 121, and is further connected to the (+) terminal of anoperational amplifier 122. The (−) terminal of the operational amplifier122 is connected to the source of the FET 3 a, and its output terminalis connected to the base of the transistor 120. The emitter of thetransistor 120 is connected to the (−) terminal of a comparator 123, andthe (+) terminal of the comparator 123 is connected to a voltage source124 for supplying reference voltage for comparison. The output signal ofthe comparator 123 is supplied to either input terminal of an AND gate126 through a filter 125.

The AND gate 126 is so constructed that the following is implemented.When the output signal of the comparator 23 is at high level, it outputsa gate signal UH, outputted by the drive control circuit 4, to the FETs3 a and 107. When the output signal transitions to low level, itinhibits the output of the gate signal UH. When a gate driving signal ofhigh level is supplied to the FET 113, the FET 113 is turned on and, asa result, the transistor 114 is also turned on. Thus, a gate drivingvoltage relative to the source of the FET 107 is applied to the gates ofthe FETs 3 a and 107, the FETs 3 a and 107 are turned on again.

The FETs 3 a and 107 are in a current mirror configuration, and theirsource voltages become equal to each other due to the operation(imaginary shorting) of the operational amplifier 122. Even though theresistor 121 is connected to the current sensing FET 107, therefore,their current ratio is kept as specified. When the FETs 3 a and 107 areturned on, the current supplied to the FET 107 flows to the resistor 121by way of the diode 119 and the transistor 120. The terminal voltagelevel of the resistor 121 is compared with the reference voltage of thevoltage source 124 by the comparator 123.

The time constant of the filter 125 is so set that the following isimplemented as illustrated later in FIG. 14. Noise with a frequencyhigher than the off time Toff when a driving current is interrupted bythe AND gate 126 is cut.

Operation of this embodiment is described with reference to FIG. 14 toFIG. 17. The drive control circuit 4 carries out processing illustratedin FIG. 17, which is similar to that of the first embodiment (FIG. 2),when the motor 2 is started. Part of the processing includes thatcarried out by hardware. The drive control circuit 4 excites thewindings 2U, 2V, 2W of the motor 2 by direct current to position itsrotor (S1). Then, the windings 2U, 2V, 2W are energized according to apredetermined commutation pattern, and thus the motor 2 is started byforced commutation (S2).

The drive control circuit 4 is so constructed that, when forcedcommutation is carried out, it performs advanced energization, that is,energization at advanced or lead angle. That is, relative to theposition of the rotor positioned at S1, commutation is carried out withtime point that is advanced by 30° from normal appropriate commutationtime point. By carrying out the advanced energization when a motor 2 isstarted, the torque of the motor 2 is reduced. Therefore, the effect ofsuppressing the occurrence of over-speed is obtained.

When the number of revolutions of the motor 2 is increased to somedegree after it is started, induced voltage developed in the windings2U, 2V, 2W can be observed. Consequently, the drive control circuit 4changes the driving scheme for the motor 2 to sensorless mode (S3). Thatis, a commutation pattern signal for the inverter unit 3 is generatedbased on the comparison signals PU, PV, PW, and gate signals UH to WLare outputted to the gates of the individual FETs 3 a to 3 f. Theenergization phase angle in sensorless mode is advanced by 30° relativeto the zero-crossing point of induced voltage.

When forced commutation is carried out at S2, the output signal of thecomparator 123 varies in the gate drive circuit 5 a according to thecurrent supplied to the motor 2 detected by the FET 107. The referencevoltage of the voltage source 124 is set to such a level that anexcessive current supplied when the motor 2 is started is limited asillustrated in FIG. 14. In this embodiment, it is set to a voltageequivalent to a current of 2 A, for example.

FIG. 15 illustrates voltages Vu to Vw of the respective phases and amotor current Im observed when a current supplied when the motor 2 isactually started is limited to 2 A. As illustrated in FIG. 15, (d), thecurrent Im passing when the motor 2 is rotating in a normal is less than1 A. The limit level of 2 A provides an upper limit set with respect toa current at too large a level passing only at the time of starting.

When the motor current Im exceeds the limit level, the output current ofthe comparator 123 changes to low level, and the AND gate 126 preventsthe output of the gate signal UH. Thus, the high-side FETs 3 a, 3 c, 3 eof the inverter unit 3 are turned off, and energization of the motor 2is stopped. As a result, the detected current value lowers, and theoutput current of the comparator 123 returns to high level. Inconjunction therewith, the AND gate 126 resumes the output of the gatesignal UH and the motor 2 is energized.

Change in the detected current is provided with a predetermined gradientby the inductance of the windings 2U to 2W of the motor 2. Asillustrated in FIG. 14, the detected current at the time of start varieslike a saw-tooth wave in proximity to the limit level and the current islimited.

FIG. 16 illustrates change in starting time (ms) observed in a casewhere a current is not limited when the motor 2 is started and in thecases where a current is limited to the limit levels of 1 A, 2 A, and 4A. The “starting time” cited here is defined as a time until therotation of the motor 2 reaches 90% of its normal number of revolutions(e.g., 10,000 rpm). The horizontal axis represents the initial position(deg) of the rotor.

When this initial position changes, the starting time may also vary.When the limit level is set to 1 A, this limit level is too low, andrequired starting torque cannot be obtained. The starting time is 100 msover the entire range of initial position, and this is much greaterthan, for example, 70 ms, which is a standard value required fromproducts. In the case of “No limit” and in the cases where the currentis limited to 2 A and 4 A, the starting time is significantly lower thanthe above required standard over the entire range of initial position.

The three cases where the starting time is shorter than the requiredstandard will be evaluated. In the case of the limit level of 2 A, thestarting time is 25 ms over the entire range of initial position. In thecases of “No limit” and the limit level of 4 A, the starting time may beshorter than in the case of the limit level of 2 A depending on theinitial position. However, the worst values (30 ms) in both cases arelarger than in the case of the limit level of 2 A. Therefore, the caseof the limit level of 2 A is considered to be most favorable forproducts.

In some other examples of measurement, the starting time is longer inthe case of “No limit” where a current largely fluctuates and in thecase of the limit level of 4 A than in the case of the limit level of 2A.

According to this embodiment, the following is implemented when therotary machine driving apparatus 1 starts the brushless DC motor 2 byforced commutation. The gate drive circuits 5 limit the current suppliedto the windings 2U to 2W of the motor 2 to an upper limit level sethigher than a level at which a current is supplied when the motor 2 isin a normal or stable rotating state. Therefore, it is possible tosuppress over-speed to shorten a starting time without preventing thestable rotation of the motor.

When the drive control circuit 4 carries out forced commutation afterpositioning the rotor, it carries out control so that the energizationphase angle for the windings 2U to 2W is advanced by a predeterminedamount. Therefore, a starting time can be further shortened.

The fifth embodiment can be modified in many ways. For instance, thelimit levels for starting currents and the normal number of revolutionsmay be appropriately modified according to the rating of a motor used orthe like. Advanced energization in forced commutation may be carried outas required. The rotary machine driving apparatus is applicable not onlyto those for driving the motor of a mini disk (MD) or a hard disk drive(HDD). It can be widely utilized in applications in which it isdifficult to stop the rotation of the motor by loss of synchronism, whenthe brushless DC motor is driven by the sensorless method.

Sixth Embodiment

In a sixth embodiment illustrated in FIG. 18, a rotary machine drivingapparatus is provided for a brushless DC motor 2, which may be providedin a vehicle as a rotary machine.

The motor 2 is a three-phase motor and an actuator of a fuel pump for aninternal combustion engine mounted in a motorcycle. The three phases(U-phase, V-phase, W-phase) of the brushless motor 2 are connected withan inverter 12. The inverter 12 is a three-phase inverter and appliesthe voltage of a battery 214 to the three phases of the brushless motor2. To provide conduction between each of the three phases and thepositive pole and negative pole of the battery 214, the inverter 12 isso constructed that it includes a parallel connection unit having:switching elements SW1, SW2 (U-phase arm), switching elements SW3, SW4(V-phase arm), and switching elements SW5, SW6 (W-phase arm). Thejunction point between the switching element SW1 and the switchingelement SW2 connected in series is connected with the U-phase of thebrushless motor 2. The junction point between the switching element SW3and the switching element SW4 connected in series is connected with theV-phase of the brushless motor 2. The junction point between theswitching element SW5 and the switching element SW6 connected in seriesis connected with the W-phase of the brushless motor 2. These switchingelements SW1 to SW6 are respectively connected in parallel with flywheeldiodes D1 to D6.

The high side switching element SW1, SW3, SW5 of each arm is constructedof a P-channel MOS transistor, and the low side switching element SW2,SW4, SW6 of each arm is constructed of an N-channel MOS transistor. Theflywheel diodes D1 to D6 are constructed of parasitic diodes of the MOStransistors.

A drive control circuit 220 operates the inverter 12 and therebycontrols the output of the brushless motor 2. Specifically, the drivecontrol circuit 220 includes a driver 222, a voltage detector 228, and aswitching controller 227. The voltage detector 228 detects the voltageVB of the battery 214.

The switching controller 227 turns on and off the switching elements SW1to SW6 through the driver 222. In this example, it basically carries outswitching control by a 120°-energization method. More specifically,utilizing the time point with which the terminal voltages Vu, Vv, Vw ofthe respective phases of the brushless motor 2 become equal to theinduced voltage, the switching controller 227 detects the following. Itdetects a time (zero-crossing time) when the induced voltage becomesequal to the virtual neutral point voltage (reference voltage Vref) ofthe brushless motor 2. Then, it changes the operation of the switchingelements SW1 to SW6 with time point (specified time point) delayed fromzero-crossing time point by a predetermined electrical angle, e.g., 30degrees (°). However, when a current (amount of energization) passed tothe brushless motor 2 is limited, the period for which the switchingelements SW1 to SW6 are turned on is not set to a 120°-period. Instead,PWM control is carried out in this period.

The switching controller 227 may be constructed of a logic circuit ormay be constructed of a central processing unit and a storage unit forstoring a program.

FIG. 2 illustrates the way switching control is carried out under normalconditions. Specifically, (a) illustrates the transition of the terminalvoltages Vu, Vv, Vw of the motor 2; (b) illustrates the transition ofcomparison signals Uc, Vc, Wc; (c) illustrates the transition ofzero-crossing detection signals; (d) illustrates the transition of thevalues on various counters; and (e) illustrates the transition ofactuating signals for the switching elements SW1 to SW6. The actuatingsignals illustrated in (e) include actuating signals U+, V+, W+ for thehigh side switching elements SW1, SW3, SW5 of the respective arms andactuating signals U−, VW− for the low side switching elements SW2, SW4,SW6. In this example, the high side switching elements SW1, SW3, SW5 ofthe respective arms are P-channel transistors; therefore, the periodsfor which these actuating signals U+, V+, W+ are at logical L are theperiods for which they are on.

Upward solid lines in (d) indicate the value Cm of the zero-crossingmeasuring counter for measuring a time interval between adjacentzero-crossing times. As illustrated in the figure, the counter isinitialized each time the zero-crossing time occurs, and newly startstime counting operation. A time interval between adjacent or successivezero-crossing times has correlation with rotational speed. For thisreason, the value of the counter immediately before it is initialized(the maximum value of the counter) provides a parameter havingcorrelation with rotational speed.

Downward solid lines in (d) indicate the value Cs of a specified timepoint setting counter that counts a time required until zero-crossingtime point becomes equal to specified time point and thereby sets aspecified time point. The specified time point setting counter takes thevalue of the counter before initialization as its initial value at thezero-crossing time and decrements it. Then, it sets the time point withwhich the value is zeroed as a specified time point. At this time, thefollowing operation is performed.

When the time interval between zero-crossing time point and specifiedtime point is 30°, for example, the decrement speed is set to twice theincrement speed of the measuring counter. In consideration of that thetime interval between adjacent zero-crossing times is 60°, it can bethought that this setting makes it possible to make the time point withwhich the value Cs of the specified time point setting counter becomes 0delayed by 30° from the zero-crossing time point.

The two-dot chain lines in (d) indicate the value Cp of a permissionstart counter. The permission start counter determines the time of thebeginning of a period (permitted period) for which detection of thezero-crossing time based on the comparison of the terminal voltages Vu,Vv, Vw and the reference voltage Vref is permitted. The permitted periodis provided to avoid the following event and for other like purposes. Ina period for which a current is supplied through the diodes D1 to D6,the terminal voltages Vu, Vv, Vw become equal to the reference voltageVref and thus this occasion is erroneously determined to be thezero-crossing time. This counter also takes the value of the counterbefore initialization as its initial value at the zero-crossing time anddecrements it. Then, it sets the time point with which the value iszeroed as the time of the beginning of a permitted period. When the timeof the beginning of a permitted period is set to a time at 45° from thezero-crossing time, for example, the decrement speed can be set to 3/2times the increment speed of the measuring counter.

The one-dot chain lines in (d) indicate the value Cps of a permittedperiod setting counter for determining the above permitted period. Whenthe value of the permission start counter is zeroed, the permittedperiod setting counter takes the value of the measuring counter beforethe previous initialization as its initial value and decrements it. Itsets the period until the value is zeroed as the permitted period. Whenthe permitted period is a period of 30°, for example, the decrementspeed can be set to twice the increment speed of the measuring counter.

In the period for which the value of the permitted period settingcounter is not less than zero, the comparison signals Uc, Vc, Wc aremade valid. When the comparison signals Uc, Vc, Wc are inverted in thisperiod, the zero-crossing detection signals of the corresponding phasesare inverted. At the zero-crossing time when the zero-crossing detectionsignal is inverted, the decrement of the specified time point settingcounter is started. When its value is zeroed, the operation of theswitching elements SW1 to SW6 is changed.

The switching control processing in this embodiment is described nextwith reference to FIG. 20 and FIG. 21. The processing of FIG. 21 forsetting the counter values on the above four counters of is repeatedlycarried out by the drive control circuit 220, for example, in apredetermined cycle.

This series of processing is carried out as follows. At S10, it ischecked whether or not the value Cps of the permitted period settingcounter is equal to or higher than zero. When it is determined that thevalue is not less than zero, it is checked at S12 whether or not any ofthe comparison signals Uc, Vc, Wc has been changed or inverted. Thisprocessing is for detecting the zero-crossing time. When it isdetermined at S12 that any of the comparison signals has been changed,the current value Cm of the measuring counter is taken as the maximumvalue of the counter at S14. At S16, subsequently, the maximum value ofthe counter is taken as the values Cs and Cps of the specified timepoint setting counter and the permitted period setting counter. At S18,the measuring counter is initialized (Cm=0).

When a negative determination is made at S10 or S12, the measuringcounter (Cm) is incremented at S20. At the same time, the permissionstart counter (Cp), permitted period setting counter (Cps), andspecified time point setting counter (Cs) are decremented. At S22,subsequently, it is checked whether or not the value Cp of thepermission start counter is zero. This processing is for checkingwhether or not it is the time of the beginning of a permitted period.When it is determined that the value Cp of the permission start counteris zero, the maximum value Cm of the counter is taken as the value Cpsof the permitted period setting counter at S24. Hereafter, detection ofthe zero-crossing time based on the comparison signals Uc, Vc, Wc ispermitted until the value Cps of the permitted period setting counter iszeroed.

When a negative determination is made at S22 or when the processing ofS18 or S24 is completed, this series of processing is once terminated.

Changing the state of the switching elements SW1 to SW6 to ON is carriedout by the processing illustrated in FIG. 21. This processing isrepeatedly carried out by the drive control circuit 220, for example, ina predetermined cycle.

At S30, it is checked whether or not the value Cs of the specified timepoint setting counter is zero. This processing is for determiningwhether or not the specified time point has occurred. When it isdetermined that the value Cs of the specified time point setting counterhas been zeroed, the operating state of the switching elements SW1 toSW6 is changed at S32. In this example, the operating state is changedas follows. When the switching elements SW1, SW4 are ON before change,the operating state is so changed that the switching elements SW1, SW6are brought into ON. When the switching elements SW1, SW6 are ON beforechange, the operating state is so changed that the switching elementsSW3, SW6 are brought into ON. When the switching elements SW3, SW6 areON before change, the operating state is so changed that the switchingelements SW2, SW3 are brought into ON. When the switching elements SW2,SW3 are ON before change, the operating state is so changed that theswitching elements SW2, SW5 are brought into ON. When the switchingelements SW2, SW5 are ON before change, the operating state is sochanged that the switching elements SW4, SW5 are brought into ON. Whenswitching elements SW4, SW5 are ON before change, the operating state isso changed that the switching elements SW1, SW4 are brought into ON.

In this embodiment, switching control by a 120°-energization method iscarried out by brining the time point with which the switching elementsSW1 to SW6 are changed into one-to-one correspondence with zero-crossingtime point.

In a vehicle, the voltage of the battery 214 is prone to fluctuate. Whenthe voltage of the battery 214 fluctuates, the rotational speed of thebrushless motor 2 changes. At this time, the time interval betweenadjacent zero-crossing times (the maximum value of the counter) cannotaccurately represent the rotational speed in proximity to the presentzero-crossing time. Therefore, a permitted period cannot be set in adesired electrical angle range depending on the above time interval. Forthis reason, when the brushless motor 2 is accelerated, for example,there is a possibility that the zero-crossing time occurs in advance ofthe permitted period. When the brushless motor 2 is decelerated, forexample, there is a possibility that the zero-crossing time occursbehind the permitted period.

In this embodiment, to cope with this, the setting of a permitted periodis corrected in correspondence with change in the rotational speed ofthe brushless motor 2. In consideration of that rotational speed ischanged by change in the voltage VB of the battery 214, specifically,the setting of a permitted period is corrected in correspondence withchange in the voltage of the battery 214.

This correction to the setting of a permitted period is carried out asillustrated in FIG. 22. This processing is repeatedly carried out by thedrive control circuit 220, for example, in a predetermined cycle.

At S40, the voltage VB of the battery 214 is acquired. At S42,subsequently, it is checked whether or not a variation ΔVB in thevoltage VB of the battery 214 is equal to or higher than a firstthreshold value α. This processing is for determining whether or not thepresent situation is a possible situation in which the following takesplace. As a result of the brushless motor 2 being accelerated, thezero-crossing time occurs ahead of the permitted period determined bythe rotational speed. This threshold value α is set based on the minimumvalue at which the above situation occurs. When it is determined thatthe variation ΔVB is equal to or higher than the threshold value α, thecount speed of the permission start counter and the permitted periodsetting counter is increased at S44. As illustrated in FIG. 23,specifically, the count speed is increased with increase in thevariation ΔVB. In this example, the following measure can be taken. Acorrection coefficient is predetermined for each discrete value ofvariation ΔVB, and the count speed is changed stepwise. Instead, thecount speed may be continuously changed according to the variation ΔVB.This processing is for implementing the following in a situation inwhich the rotational speed of the brushless motor 2 is increased. Apermitted period is set in substantially the same electrical angle rangeas when the rotational speed is constant.

When the variation ΔVB is less than the threshold value α, it isdetermined at S46 whether or not the variation ΔVB is equal to or lowerthan a second threshold value β. This processing is for determiningwhether or not the present situation is a possible situation in whichthe following takes place. As a result of the brushless motor 2 beingdecelerated, the zero-crossing time occurs behind a permitted perioddetermined by the rotational speed. This threshold value β is set basedon the maximum value at which the above situation occurs. When it isdetermined that the variation ΔVB is equal to or lower than thethreshold value β, the count speed of the permission start counter andthe permitted period setting counter is decreased at S48. As illustratedin FIG. 23, specifically, the count speed is decreased with decrease inthe variation ΔVB. The count speed is decreased when the variation takesa negative value and with increase in its absolute value. Thisprocessing is for implementing the following in a situation in which therotational speed of the brushless motor 2 is reduced. A permitted periodis set in substantially the same electrical angle range as when therotational speed is constant.

When it is determined at S46 that the variation ΔVB is larger than thethreshold value β or when the processing of S44 or S48 is completed,this series of processing is once terminated. According to the aboveprocessing, the zero-crossing time can be appropriately detected evenwhen the rotational speed of the brushless motor 2 is changed byvariation in the voltage VB of the battery 214.

There are cases where the rotational speed of the brushless motor 2based on a detected value of zero-crossing time point becomesexcessively high or low. This leads to a state in which it is difficultto appropriately control the rotating state of the brushless motor 2(loss of synchronism state). In this state, it is desirable to restartthe brushless motor 2. Before this state occurs, the rotational speed ofthe brushless motor 2 is continuously increased or reduced. For thisreason, a phenomenon that the zero-crossing time deviates from apermitted period tends to consecutively occur more than once. In thisembodiment, consequently, the following processing is carried out whenthe number of times when the zero-crossing time continuously occurseither ahead of or behind a permitted period becomes equal to or higherthan a threshold value. The rotating state of the brushless motor 2 isdetermined to be abnormal, and processing is carried out to restart thebrushless motor 2.

Hereafter, this processing will be described with reference to FIG. 24and FIG. 25. FIG. 24 illustrates the processing for coping with anabnormality that the zero-crossing time occurs ahead of the permittedperiod. This processing is repeatedly carried out by the drive controlcircuit 220, for example, in a predetermined cycle.

In this processing, at S50, it is checked whether or not the value Cp ofthe permission start counter is zero. This processing is for determiningwhether or not it is the time of the beginning of the permitted period.When it is determined that the value Cp of the permission start counteris zero, it is determined at S52 whether or not the logical value of thecorresponding comparison signal Uc, Vc, Wc is normal. This processing isfor determining whether or not the zero-crossing time has occurred aheadof the permitted period.

As illustrated in FIG. 19, the zero-crossing time occurs every 60°.Whether the induced voltage of any phase crosses the reference voltageVref in its rising process or falling process has 360°-periodicity. Forthis reason, in which phase the present zero-crossing time occurs andwhether the induced voltage of that phase is in its rising process orfalling process can be identified according to the following: in whichphase the previous zero-crossing time occurred and whether the inducedvoltage of that phase was in its rising process or falling process. Morespecifically, in the example illustrated in FIG. 19, it will be assumedthat the zero-crossing time when the terminal voltage Vv of V-phasecrosses the reference voltage Vref in its falling process. In this case,it can be predicated that the next zero-crossing time will occur inU-phase and the zero-crossing time occurs in the rising process of theterminal voltage Vu of that phase. For this reason, it can be thoughtthat, in the permitted period, the comparison signal Uc of U-phase isinverted from logical L to logical H. Meanwhile, if the comparisonsignal Uc of U-phase has been already at logical H when the value of thepermission start counter is zeroed, it can be determined that thezero-crossing time has occurred ahead of the permitted period.

When the logical value of a comparison signal of a phase in which thezero-crossing time is presumed to occur in the permitted period isdetermined to be abnormal, the processing proceeds to S54. At S54, it isdetermined that the zero-crossing time point is excessively advanced.Then, the value of the counter is substituted for the values Cp on thepermission start counter and the specified time point setting counterCs. Thus, the time point with which the value Cp of the permission startcounter is zeroed is taken as zero-crossing time point to set specifiedtime point and the like. This processing is for avoiding the followingeven when an erroneous determination is made at S52: the setting ofspecified time point and the like is excessively shifted from normaltime point. At S56, subsequently, the measuring counter is initialized.

At S58, it is checked whether or not the determination of excessiveadvance is continued, that is, the previous zero-crossing time alsooccurred ahead of the permitted period. When the previous zero-crossingtime also occurred ahead of the permitted period, an excessive advancecounter is incremented at S60. The excessive advance counter isconfigured to count a number of times Ca when the zero-crossing timecontinuously occurs ahead of the permitted period. At S62, subsequently,it is checked whether or not the value Ca of the excessive advancecounter has become equal to a threshold value MAX. This processing isfor determining whether or not the rotating state of the brushless motor2 is abnormal and it is difficult to control the rotating state. Thisthreshold value MAX is set to a value larger than an estimated number oftimes when the zero-crossing time will occur ahead of permitted periodat start of the brushless motor 2. When it is determined that the valueof the excessive advance counter is equal to the threshold value MAX,restart processing (restoration processing) for the brushless motor 2 iscarried out at S64. At the same time, the excessive advance counter isinitialized.

When a negative determination is made at S58, the excessive advancecounter is initialized at S66. This processing is for avoiding thefollowing when the zero-crossing time occurs ahead of the permittedperiod due to start of the brushless motor 2, the influence of noise orthe like, load variation, or the like. The value Ca of the excessiveadvance counter is accumulated, and it is eventually determined to beabnormal and restart processing is carried out. When a negativedetermination is made at S50 or S52 or when the processing of S64 or S66is completed, this series of processing is once terminated.

FIG. 25 illustrates the processing for coping with an abnormality thatthe zero-crossing time occurs behind a permitted period. That is, thezero-crossing time is delayed. This processing is repeatedly carried outby the drive control circuit 220, for example, in a predetermined cycle.This series of processing is carried out as follows.

At S70, it is checked whether or not the value Cps of the permittedperiod setting counter is zero. This processing is for determiningwhether or not it is the time of the end of the permitted period. Whenit is determined that the value Cps of the permitted period settingcounter is zero, it is determined at S72 whether or not an affirmativedetermination was made at S52 in FIG. 24 and the zero-crossing time hasbeen already detected. This processing is for determining whether or notthe zero-crossing time occurs behind the permitted period. Morespecifically, when the zero-crossing time has not occurred ahead of thepermitted period and does not occur in the permitted period, either, itcan be expected that it will be delayed and occur behind the permittedperiod.

When a negative determination is made at S72, processing similar withthat of S54 to S66 in FIG. 24 is carried out at S74 to S86, in which adelay is counted as the delay value Cd by using a delay counter.

In this embodiment, a loss of synchronism state is determined based onthat the zero-crossing time continuously occurs ahead of or behind thepermitted period. For this reason, a state in which the zero-crossingtime is incidentally caused to deviate from the permitted period by theinfluence of noise or the like can be discriminated from a loss ofsynchronism state. Further, setting is so made that the permitted periodis at a predetermined electrical angle regardless of fluctuation in thevoltage of the battery 214. Therefore, a loss of synchronism state canbe prevented from being determined due to fluctuation in the voltage ofthe battery 214.

According to the sixth embodiment, the following advantages can beprovided.

(1) When the number of times when the zero-crossing time continuouslyoccurs either ahead of or behind the permitted period becomes equal toor higher than a threshold value MAX, the brushless motor 2 isdetermined to be abnormal. Thus, when rotational fluctuation temporarilyoccurs due to load variation or the like or any other like event occurs,that can be prevented from being determined to be abnormal.

(2) When it is determined that the zero-crossing time has occurred aheadof the permitted period, the time of the beginning of the permittedperiod is assumed to be the zero-crossing time to set a specified timepoint. Thus, even when determination is erroneous, it can be avoidedthat a specified time point is too inappropriately set.

(3) When it is determined that the zero-crossing time occurs behind thepermitted period, the time of the end of the permitted period is assumedto be the zero-crossing time to set the specified time point. Thus, evenwhen determination is erroneous, it can be avoided that a specified timepoint is too inappropriately set.

(4) Based on the value of a comparison signal at the time of thebeginning of the permitted period, it is checked whether or not thezero-crossing time has occurred ahead of the permitted period. Based onthe presence or absence of change in a comparison signal in thepermitted period, it is checked whether or not the zero-crossing timeoccurs behind the permitted period. Thus, these determinations can beappropriately made.

(5) According to change in the rotational speed of the brushless motor2, the setting of the permitted period based on the values on thepermission start counter and the permitted period setting counter iscorrected. This makes it possible to accurately set a permitted periodin a desired electrical angle range regardless of any change inrotational speed, and to enhance the robustness of control on therotating state of the brushless motor 2.

(6) Change in rotational speed is detected through voltage variation ΔVBin the voltage VB of the battery 214. Thus, change in rotational speedcan be appropriately detected. Especially, the following advantage isprovided by detecting a rotational speed based on the voltage VB of thebattery 214. When the rotating state becomes abnormal regardless offluctuation in the voltage VB of the battery 214, the setting of thepermitted period is kept unchanged. For this reason, the setting of thepermitted period based on the time interval between zero-crossing timescan be corrected only when the voltage VB of the battery 214 fluctuates.

Seventh Embodiment

In a seventh embodiment, the acceleration of the brushless motor 2 isdetected based on a detected value of zero-crossing time, and thesetting of a permitted period is corrected based on this acceleration.FIG. 26A illustrates processing for correcting the setting of apermitted period. This processing is repeatedly carried out by the drivecontrol circuit 220, for example, in a predetermined cycle. This seriesof processing is carried out as follows.

At S90, the acceleration A of the brushless motor 2 is calculated basedon the previous maximum value of the counter and the present maximumvalue of the counter. The maximum value may be determined based on thevalue Cm (FIG. 19) of the measuring counter. The maximum value of thecounter is for counting the time interval between zero-crossing times,and has correlation with the instantaneous rotational speed betweenzero-crossing times. For this reason, these two values, the previousmaximum value of the counter and the present maximum value of thecounter, are values at two different points of time with respect toinstantaneous rotational speed. For this reason, the acceleration A canbe calculated from them.

At S92, subsequently, it is checked whether or not the acceleration A isequal to or higher than a threshold value Amax. This processing is fordetermining whether or not the zero-crossing time occurs ahead of thepermitted period determined by its rotational speed as a result of thebrushless motor 2 being accelerated. When it is determined that theacceleration is equal to or higher than the threshold value Amax, thesame processing as that of S44 in FIG. 22 is carried out at S94. Thatis, the count speed of the permission start counter and the permittedperiod setting counter is increased with increase in the acceleration Aas illustrated in FIG. 26B.

When a negative determination is made at S92, meanwhile, it isdetermined at S96 whether or not the acceleration A is equal to or lowerthan a threshold value Amin. This processing is for determining whetheror not the zero-crossing time occurs behind the permitted perioddetermined by its rotational speed as a result of the brushless motor 2being decelerated. When it is determined that the acceleration is equalto or lower than the threshold value Amin, the same processing as thatof S48 in FIG. 22 is carried out at S98. That is, the count speed of thepermission start counter and the permitted period setting counter isreduced with reduction in the acceleration A. The count speed is reducedwhen the acceleration takes a negative value and with increase in itsabsolute value.

When a negative determination is made at S96 or when the processing ofS94 or S98 is completed, this series of processing is once terminated.

According to this embodiment described above, the following advantagecan be provided in addition to the advantages of the sixth embodimentdescribed under (1) to (5) above.

(7) Based on the result of detection of the zero-crossing time,information pertaining to change in the rotational speed of thebrushless motor 2 is extracted. Thus, change in rotational speed can beappropriately determined.

Eighth Embodiment

In the sixth embodiment, when the zero-crossing time occurs ahead of thepermitted period, the time of the beginning of the permitted period isassumed to be the zero-crossing time to set a specified time point. Inthis case, however, when the zero-crossing time continuously occursahead of the permitted period, the specified time point is continuouslydelayed from appropriate time point, and this degrades the efficiency ofthe control on the output of the brushless motor 2.

Therefore, in an eighth embodiment, a most advanced time that can beassumed to be the zero-crossing time and adopted is set ahead of thetime of the beginning of permission time point. When the zero-crossingtime occurs ahead of the permitted period, the zero-crossing time is setto a time between the most advanced time and the time of the beginningof the permitted period (including the most advanced time and the timeof the beginning) at which the difference between it and thezero-crossing time is minimized.

As illustrated in FIG. 27A and FIG. 27B, the most advanced time is setto a time point with which the value Cma of a maximum advance counterbecomes 0. The maximum advance counter starts decrementing from itsinitial value for which the value of the counter at the zero-crossingtime is taken. By making the decrement speed of the maximum advancecounter faster than the decrement speed of the permission start counter,the most advanced time at which the value of the maximum advance counteris zeroed can be set ahead of the time of the beginning of a permittedperiod. This most advanced time is predetermined as time point withwhich a predetermined electrical angle lapses after the zero-crossingtime according to the specifications of the brushless motor 2 or thelike.

FIG. 28 illustrates processing for coping with an abnormality that thezero-crossing time occurs ahead of the permitted period. This processingis repeatedly carried out by the drive control circuit 220, for example,in a predetermined cycle. In FIG. 28, the same processing as thatillustrated in FIG. 24 will be identified with the same step number forsimplicity.

When a negative determination is made at S52, that is, it is determinedthat the zero-crossing time has occurred ahead of the permitted period,the processing proceeds to S100. At S100, it is checked whether or notan output level change time of the corresponding one of the comparisonsignals Uc, Vc, Wc occurs ahead of or before the most advanced time(including the most advanced time). This processing can be carried out,for example, according to whether or not the logical value of thecorresponding one of the comparison signals Uc, Vc, Wc when the value ofthe maximum advance counter becomes 0 is abnormal. When it is determinedthat the change time occurs ahead of the most advanced time, thefollowing processing is carried out at S102: in addition to processingfor determination of excessive advance of zero-crossing time point andprocessing for substituting the value Cm of the counter for the value Cpof the permission start counter, processing for assuming the mostadvanced time to be the zero-crossing time to set a specified timepoint. That is, the value Cs of the specified time point setting counteris so set that the following is implemented based on the period from theprevious zero-crossing time to the zero-crossing time assumed this time.The specified time point setting counter takes a value corresponding tothe time required from the present time to the specified time point.

When it is determined at S100 that the change time occurs behind themost advanced time, the following processing is carried out at S104 inaddition to processing for determination of excessive advance ofzero-crossing time point and processing for substituting the value Cm ofthe counter for the value Cp of the permission start counter: processingfor assuming the change time of the corresponding one of the comparisonsignals Uc, Vc, Wc to be the zero-crossing time in the period from themost advanced time to the time of the beginning of a permitted periodand thereby setting a specified time point. That is, the value Cs of thespecified time point setting counter is so set that the following isimplemented based on the period from the previous zero-crossing time tothe zero-crossing time assumed this time. The specified time pointsetting counter takes a value corresponding to the time required fromthe present time to the specified time point.

When the processing of S102 or S104 is completed, the processing of S56to S64 in FIG. 6 is carried out.

According to this embodiment, the following advantage is brought. Evenwhen the zero-crossing time occurs before the time of the beginning of apermitted period, a specified time point can be set using a time pointapproximate to the actual zero-crossing time point as much as possibleby setting the most advanced time. For this reason, degradation in theefficiency of control on the output of the brushless motor 2 can befavorably suppressed. Further, based on that the zero-crossing timecontinuously occurs ahead of the permitted period, any abnormality inthe rotating state is determined; therefore, this determination can alsobe appropriately made.

The sixth to eighth embodiments may be modified as described below.

In the sixth embodiment, the count speed of the permission start counterand the permitted period setting counter is corrected according to thevariation ΔVB in the voltage of the battery 214. As illustrated in FIG.29, instead, the count speed may be corrected according to twoparameters: the voltage VB of the battery 214 and its variation ΔVB.FIG. 29 is a data map defining the relation between these two parametersand the count speed correction coefficient Aij. The reason why thevoltage VB of the battery 214 is used as a parameter is as follows. Evenwhen the variation ΔVB in the voltage of the battery 214 is identical,the degree of change in the rotational speed of the brushless motor 2can differ depending on the voltage VB of the battery 214. For thisreason, use of two parameters makes it possible to more accuratelydetect rotational fluctuation in the brushless motor 2 caused byfluctuation in the voltage VB of the battery 214.

The parameters for detecting change in the rotational speed of thebrushless motor 2 are not limited to those described in relation to theabove embodiments and their modifications. For instance, the magneticflux in the brushless motor 2 is weakened and its rotational speed isincreased with increase in the temperature Tm of the brushless motor 2.In consideration of this, variation in the temperature (or itsequivalent) of the brushless motor 2 may be used. Alternatively, using amap defining the relation of the count speed correction coefficient Bijto the temperature Tm of the brushless motor 2 and variation ΔVB in thevoltage of the battery 214, which is illustrated in FIG. 30, change inrotational speed may be detected based on these two parameters.

In the sixth embodiment, the processing of FIG. 22 need not be carriedout. A loss of synchronism state can be discriminated from at least theinfluence of rotational fluctuation due to start or incidental noise byadjusting the threshold value MAX in FIG. 24 or FIG. 25.

The neutral point voltage of the brushless motor 2 may be used as thereference voltage Vref in place of the virtual neutral point voltage.One half of the voltage VB of the battery 214 may be used by dividingthe voltage of the battery 214 with a resistive element.

When PWM control is used as a technique for controlling the brushlessmotor 2, for example, the following measure can be used. The period forwhich the switching elements SW1 to SW6 are ON is taken as anOn-permitted period, and the switching elements SW1 to SW6 arerepeatedly turned on and off in this period. In this case, however, therotational speed of the brushless motor 2 can vary according to the rate(duty) of on time to the sum of on time and off time. Therefore, it isdesirable to determine a mode for correcting the count speed accordingto the duty.

The time point with which a predetermined electrical angle occurs,detected based on induced voltage, is not limited to zero-crossing timepoint. For example, that found in JP 11-18478A may be adopted.

The power supply connected to the brushless motor 2 need not be thebattery 214, but a generator may be connected. The brushless motor 2need not be an actuator of an in-vehicle fuel pump, but may be anactuator of an in-vehicle cooling fan. The rotary machine need not be athree-phase brushless motor but may be a motor of any number of phases.Further, it need not be a motor and may be a generator.

Ninth Embodiment

In a ninth embodiment illustrated in FIG. 31, a brushless motor 2 is athree-phase motor and it is an actuator of a fuel pump for an internalcombustion engine mounted in a motorcycle. The three phases (U-phase,V-phase, W-phase) of the brushless motor 2 are connected with aninverter 12. This inverter 12 is a three-phase inverter and applies thevoltage VB of a battery 214 to the three phases of the brushless motor2. To provide conduction between each of the three phases and thepositive pole or negative pole of the battery 214, the inverter 12 isconstructed to include a parallel connection body having: switchingelements SW1, SW2 (U-phase arm), switching elements SW3, SW4 (V-phasearm), and switching elements SW5, SW6 (W-phase arm). The switchingelements SW1 to SW6 and diodes D1 to D6 are connected in the similarmanner as in the sixth embodiment (FIG. 18).

A drive control circuit 230 operates the inverter 12 through a driver222 and thereby controls the output of the brushless motor 2.Specifically, the drive control circuit 230 takes in comparison signalsPU, PV, PW from comparators 224, 226, 228 and operates the switchingelements SW1 to SW6 based thereon.

The comparators 224, 226, 228 are for comparing the terminal voltagesVu, Vv, Vw of respective phases with a reference voltage Vref. Thecomparator 224 compares the U-phase terminal voltage Vu of the brushlessmotor 2 with the reference voltage Vref, and outputs the result of thiscomparison as a comparison signal PU. The comparator 226 compares theV-phase terminal voltage Vv of the brushless motor 2 with the referencevoltage Vref and outputs the result of this comparison as a comparisonsignal PV. The comparator 228 compares the W-phase terminal voltage Vwof the brushless motor 2 with the reference voltage Vref and outputs theresult of this comparison as a comparison signal PW.

In this embodiment, a virtual neutral point voltage obtained by dividingthe terminal voltages Vu, Vv, Vw of the respective phases with resistiveelements RU, RV, RW is used for the reference voltage Vref. The reasonfor this is as follows. In the in-vehicle battery 214, its voltage valueis prone to rapidly fluctuate, while the rate of change in inducedvoltage in the brushless motor 2 tends to become slower than the rate ofchange in the voltage of the battery 214. For this reason, when thevoltage of the battery 214 rapidly rises, ½ of the amplitude of inducedvoltage does not become equal to ½ of the voltage of the battery 214.For this reason, when ½ of the voltage of the battery 214 is used forthe reference voltage, comparison by the comparators 224, 226, 228cannot be appropriately carried out with the voltage of the battery 214fluctuating.

The drive control circuit 230 turns on and off the switching elementsSW1 to SW6 through the driver 222. In this example, it basically carriesout switching control by a 120°-energization method. Using the abovecomparison signals PU, PV, PW, it detects time point (zero-crossing timepoint) with which the induced voltage of each phase of the brushlessmotor 2 becomes equal to the reference voltage Vref of the brushlessmotor 2. Then, it changes the operation of the switching elements SW1 toSW6 with time point (specified time point) delayed from thezero-crossing time point by a predetermined electrical angle (e.g.,30°).

The drive control circuit 230 may be constructed by logic circuits ormay be constructed by a central processing unit and a storage unit forstoring a program.

The switching control is carried out in 120°-energization control asillustrated in FIG. 32. Specifically, (a) illustrates the transition ofthe terminal voltages Vu, Vv, Vw indicated by solid lines and thereference voltage Vref by one-dot chain lines. In this embodiment, thevirtual neutral point voltage is used as the reference voltage Vref.Though, in actuality, the reference voltage Vref fluctuates, it isconsidered to be constant here for the sake of simplicity. (b)illustrates the results of comparison of the terminal voltages Vu, Vv,Vw with the reference voltage Vref with respect to magnitudes(comparison signals PU, PV, PW). (c) illustrates the transition of alogically combined signal PS of the comparison signals PU, PV, PW. 2(d)illustrates the transition of a logically combined signal (expectationsignal Se) of the comparison signals PU, PV, PW expected when thezero-crossing time occur while the switching elements SW1 to SW6 are inoperation. FIG. 2( e) illustrates the transition of a detection signalQs with respect to zero-crossing time point. This is a signal whoserising edges and falling edges are synchronized with zero-crossing timepoint. (f) illustrates the transition of the values on various counters,and (g) illustrates the transition of actuating signals for theswitching elements SW1 to SW6. The actuating signals illustrated in (g)include actuating signals U+, V+, W+ for the high side switchingelements SW1, SW3, SW5 of the arms of the respective phases andactuating signals U−, VW− for the low side switching elements SW2, SW4,SW6 of the arms of the respective phases. The high side switchingelements SW1, SW3, SW5 of the arms of the respective phases areP-channel transistors; therefore, the periods for which these actuatingsignals U+, V+, W+ are at logical L are the periods for which they areON.

The combined signal PS is a three-bit signal, and the respective logicalvalues of the comparison signals PU, PV, PW respectively agree with thelogical values of its highest-order (most significant) bit, intermediatebit, and lowest-order (least significant) bit. That is, when thecomparison signal PU is at logical H the highest-order bit is set to 1;and when the comparison signal PU is at logical L the highest-order bitis set to 0. For this reason, when the comparison signals PU, PV PW arerespectively at H, L, and H, for example, the combined signal PS is setto 101 in binary notation and 5 in decimal notation. In FIG. 32, boththe combined signal PS and the expectation signal Se are represented indecimal notation.

The solid line in (f) indicate the value Cm of a measuring counter formeasuring a time interval between adjacent zero-crossing times. Themeasuring counter is initialized each time the zero-crossing timeoccurs, and newly starts time counting operation. A time intervalbetween adjacent zero-crossing times has correlation with rotationalspeed. For this reason, the value of the counter immediately before itis initialized (the maximum value of the counter) provides a parameterhaving correlation with rotational speed.

The one-dot chain lines in (f) indicate the value Cs of a specified timepoint setting counter that counts a time required until zero-crossingtime point becomes equal to specified time point and thereby sets aspecified time point. The specified time point setting counter takes thevalue of the counter before initialization as its initial value at thezero-crossing time and decrements it. Then, it sets the time point withwhich the value is zeroed as a specified time point. At this time, thefollowing operation is performed. When the time interval betweenzero-crossing time point and specified time point is 30°, for example,the decrement speed is set to twice the increment speed of the measuringcounter. In consideration of that the time interval between adjacentzero-crossing times is 60°, it can be thought that this setting makes itpossible to delay the time point with which the value of the specifiedtime point setting counter becomes 0 by 30° from the zero-crossing timepoint.

The two-dot chain lines illustrated in (f) indicate the value Cmk of amasking period counter. The masking period counter determines a period(masking period) for which detection of the zero-crossing time based onthe comparison of the terminal voltages Vu, Vv, Vw with the referencevoltage Vref is inhibited (disabled). This counter is for preventing thefollowing event. When the terminal voltages Vu, Vv, Vw agree with thereference voltage Vref during a period for which a current is suppliedthrough the diodes D1 to D6, the zero-crossing time is erroneouslydetected. This counter also takes the value of the counter beforeinitialization as its initial value at the zero-crossing time anddecrements it. Then, it sets the period before the value is zeroed as amasking period. When the masking period is set to a period from thezero-crossing time to 450, for example, the decrement speed can be setto 3/2 times the increment speed of the measuring counter.

When the value of the masking period counter is zeroed, the comparisonsignals PU, PV, PW and the combined signal PS are enabled. When thecombined signal PS agrees with the expectation signal Se during thisperiod, the detection signal Qs is inverted. At the zero-crossing timewhen the detection signal Qs is inverted, the specified time pointsetting counter starts decrementing. When its value is zeroed, theoperation of the switching elements SW1 to SW6 is changed.

As illustrated in FIG. 32, the specified time point with which theswitching elements SW1 to SW6 are turned on and the zero-crossing timepoint have one-to-one correspondence with each other. For this reason,the behavior of the terminal voltages Vu, Vv, Vw of the respectivephases is uniquely determined according to the operating state of theswitching elements SW1 to SW6. Consequently, the above expectationsignal Se can be uniquely determined.

If the battery 214 and the inverter 12 are insufficiently connected orany other like event occurs, the following phenomenon can take place.Because of transmission of vibration of the vehicle to the battery 214or any other reason, the battery 214 and the inverter 12 may beinstantaneously disconnected from each other and then conduction isestablished between them again. If power supply to the brushless motor 2is temporarily interrupted at this time, the rotational speed of thebrushless motor 2 is reduced. If fuel discharged from a fuel tank to theupstream side by a fuel pump driven by the motor 2 flows back at thistime, force on the reverse rotation side is exerted on the brushlessmotor 2. This may eventually cause reverse rotation of the motor 2. Ifin this situation the switching elements SW1 to SW6 are operated asunder normal conditions, a problem may arise. For example, anoscillation phenomenon that the brushless motor 2 repeats normalrotation and reverse rotation occurs, and it is difficult to control thebrushless motor 2 in a proper rotating state.

The reverse rotation of the brushless motor 2 can be appropriatelydetected based on the above combined signal PS composed of three bits.As illustrated in FIG. 33, when the brushless motor 2 is normallyrotating in the forward direction, time-series data on the combinedsignal PS should agree with time-series data on the expectation signalSe. When the brushless motor 2 is rotating in reverse, meanwhile,time-series data on the combined signal PS should agree with dataobtained by time-reversing, that is, reversing the order of arrangement,time-series data on the expectation signal Se as illustrated in FIG. 34.For this reason, the reverse rotation of the brushless motor 2 can bedetected based on the combined signal PS.

When the rotating state of a brushless motor 2 becomes abnormal, all theswitching elements SW1 to SW6 are turned off and the operation waits forthe brushless motor 2 to stop. Then, the brushless motor 2 is restarted.In this case, however, it takes a long time to restore the brushlessmotor 2 to a normal state.

To cope with this, the following processing is carried out in thisembodiment. When it is detected that the brushless motor 2 is rotatingin reverse, processing is carried out to forcibly stop the rotation ofthe brushless motor 2 and then restart processing is carried out.

FIG. 35 illustrates processing for restarting the brushless motor 2 inthis embodiment. This processing is repeatedly carried out by the drivecontrol circuit 230, for example, in a predetermined cycle.

This series of processing is carried out as follows. At S210, it ischecked whether or not the value Cmk of the masking period counter iszero. When it is determined that the value Cmk of the masking periodcounter is zero, it is determined at S212 whether or not the combinedsignal PS of the comparison signals PU, PV, PW has changed. Thisprocessing is for determining whether or not it is the zero-crossingtime point. When it is determined that the combined signal PS haschanged, it is determined at S214 whether or not the present combinedsignal agrees with the second previous expectation signal Se. Thisprocessing is for determining whether or not the brushless motor 2 isrotating in reverse. As illustrated in FIG. 33, when the brushless motor2 is rotating in reverse, time-series data on the combined signal PS isinverted. Therefore, it is presumed that the present combined signal PSagrees with the second previous expectation signal Se. When the presentcombined signal PS agrees with the second previous expectation signalSe, it is determined at S16 that the brushless motor 2 is rotating inreverse.

At S218, subsequently, processing is carried out to forcibly stop therotation of the brushless motor 2. Specifically, the switching elementsSW1, SW3, SW5 or the switching elements SW2, SW4, SW6 are all turned onto short-circuit all the phases of the brushless motor 2. Thus, acurrent is supplied through the brushless motor 2 only by inducedvoltage produced in conjunction with the rotation of the brushless motor2. This current is quickly attenuated by the resistance of the currentpassage. As a result, the rotational energy of the brushless motor 2 isconverted into electrical energy and then attenuated. For this reason,the brushless motor 2 can be quickly stopped.

At S220, it is checked whether or not the rotational speed of thebrushless motor 2 is substantially zero. The rotational speed can becalculated based on time intervals between adjacent zero-crossing timepoints. This can be done using the maximum value Cm of the counter. Whenit is determined that the rotational speed is substantially zero,restart processing is carried out at S222 by operating the switchingelements SW1 to SW6 based on zero-crossing time point.

When a negative determination is made at any of S210 to S214 or when theprocessing of S222 is completed, this series of processing is onceterminated.

Thus, the zero-crossing time point is used in determination of whetheror not the rotational speed is substantially zeroed in conjunction withstopping processing. However, this may cause a problem. The virtualneutral point is used to set the reference voltage Vref. Therefore, whenthe rotational speed of the brushless motor 2 is substantially zero, theterminal voltages Vv, Vu, Vw of all the phases of the brushless motor 2can agree with the reference voltage Vref. When all the switchingelements SW1 to SW6 are once turned off to restart the motor, all of thephases are brought into a high-impedance state. Also in this case,therefore, the terminal voltages Vv, Vu, Vw of all the phases of thebrushless motor 2 can agree with the reference voltage Vref.

If noise is superimposed on the terminal voltages Vv, Vu, Vw in thesesituations, the following phenomenon takes place. The terminal voltagesVv, Vu, Vw indicated by solid lines in FIG. 36A, and the referencevoltage Vref indicated by one-chain dot lines frequently cross eachother. In reality, the reference voltage Vref also fluctuates accordingto the terminal voltages Vu, Vv, Vw; however, it is considered to beconstant here for simplicity. In this case, there is a possibility thatthe zero-crossing time point is frequently erroneously detected. In thisembodiment, to cope with this, the reference voltage Vref is subjectedto offset correction so that the following is implemented. The value ofthe reference voltage Vref and the values of the terminal voltages Vv,Vu, Vw inputted to the comparators 224, 226, 228 as illustrated in FIG.31 are made different from each other when the rotational speed issubstantially zero. That is, the signal wire for inputting the referencevoltage Vref to the comparators 224, 226, 228 is connected to thepositive pole of the battery 214 through a resistive element 30. Thus,the following can be implemented as illustrated in (b) of FIG. 35. Thereference voltage Vref obtained when the rotational speed issubstantially zero can be corrected to the positive pole side of thebattery 214 by an offset Δ with respect to the terminal voltage Vu. Inthis example, only the U-phase is illustrated.

This offset Δ is set to small an amount so that control on the brushlessmotor 2 will not be influenced. At the same time, the offset is set toan amount assumed to be required to implement the following. Theterminal voltage Vu and the reference voltage Vref are prevented fromcrossing each other, even if noise is mixed, when the rotational speedis substantially zero, as illustrated in FIG. 36B. With this setting, asillustrated in FIG. 36C, the reference voltage Vref is increased withincrease in the rotational speed. When the terminal voltage Vu rises andexceeds the reference voltage Vref, the zero-crossing time point whenthe terminal voltage Vu and the reference voltage Vref cross each otheroccurs. Thus, as illustrated in FIG. 36D with respect to the U-phase,the control under normal conditions, illustrated in FIG. 32, can becarried out.

In this embodiment, especially, degradation in the efficiency of thebrushless motor 2 is prevented by correcting the reference voltage Vref.When the terminal voltages Vu, Vv, Vw are corrected, meanwhile, thephenomenon illustrated in FIG. 36E occurs. That is, the amount offluctuation in voltage applicable to the brushless motor 2 becomes lowerthan the voltage VB between the positive pole and the negative pole ofthe battery 214, and this degrades efficiency. That is, a loss isproduced by an amount equivalent to the region hatched in FIG. 36E.

It is desirable that the offset Δ should be approximately an order ofmagnitude less than the amount VE of voltage drop observed when acurrent is supplied through the diodes D1 to D6. This makes it possibleto prevent the values of the comparison signals PU, PV, PW from becomingabnormal due to ringing noise when the operation of the switchingelements SW1 to SW6 is changed. For this reason, the following can beimplemented even when PWM control is carried out. That is, the followingcan be implemented even when, for example, a period from specified timepoint to 1200 is taken as an ON operation-permitted period and theswitching elements SW1 to SW6 are turned on and off during this period.Zero-crossing time point can be accurately detected by the methodillustrated in FIG. 32.

According to the ninth embodiment, the following advantages areprovided.

(1) When the rotational speed of the brushless motor 2 is substantiallyzeroed, the terminal voltages Vu, Vv, Vw are equal to one another. Atthis time, at least either of the values of the terminal voltages Vu,Vv, Vw and the value of the reference voltage Vref to be compared by thecomparators 224, 226, 228 is subjected to offset correction. Thesevalues are thereby made different from each other. Thus, even when noiseis mixed and thus a terminal voltage fluctuates, the occurrence of aphenomenon that the terminal voltage frequently crosses the referencevoltage can be avoided. As a result, erroneous detection ofzero-crossing time point can be favorably avoided.

(2) The above correction is carried out by the resistive element 30 thatconnects the signal wire for inputting the reference voltage Vref to thecomparators 224, 226, 228 to the positive potential of the battery 214.Thus, the reference voltage Vref can be corrected to the positivepotential of the battery 214, and further, this amount of correction canbe adjusted by the resistance value of the resistive element 30.

(4) Since the reference voltage Vref is to be corrected, the followingadvantage is brought. Degradation in the efficiency of control on thebrushless motor 2 can be suppressed as compared with cases where theterminal voltages Vu, Vv, Vw are to be corrected, and further the numberof objects to be corrected can be reduced.

(5) The virtual neutral point voltage is used for the reference voltageVref. Therefore, even when the brushless motor 2 does not have a wiringconnected to a neutral point, the reference voltage Vref can beappropriately determined.

(6) The operation of the switching elements SW1 to SW6 for starting thebrushless motor 2 at a stop is started based on a detected value ofzero-crossing time point. If noise is mixed into the terminal voltagesVu, Vv, Vw in this case, a phenomenon that the terminal voltages Vu, Vv,Vw and the reference voltage Vref frequently cross each other can occur.As a result, erroneous detection of zero-crossing time point is prone tooccur. To cope with this, this embodiment is so constructed that theabove operation and advantage can be especially favorably provided.

In the ninth embodiment, microcomputer processing may be used in placeof the comparators 224, 226, 228 to compare the terminal voltages Vu,Vv, Vw and the reference voltage Vref with each other. The signal wirefor applying the reference voltage Vref to the comparators 224, 226, 228may be grounded through a resistive element. Thus, the reference voltageVref can be corrected to the ground potential side. The construction forcorrecting the reference voltage Vref need not be that the signal wirefor applying the reference voltage Vref to the comparators 224, 226, 228is connected to a predetermined potential through a resistive element.For example, an output signal obtained by voltage converting thepositive potential of the battery 214 through an inverting amplifiercircuit or a non-inverting amplifier circuit may be applied to thesignal wire for applying the reference voltage Vref to the comparators224, 226, 228. The object to be corrected need not be the referencevoltage Vref and may be the terminal voltages Vu, Vv, Vw. Alternatively,it may be both the reference voltage Vref and the terminal voltages Vu,Vv, Vw. When the terminal voltages Vu, Vv, Vw are corrected, however, itis desirable to make their amounts of correction identical with oneanother.

Tenth Embodiment

In a tenth embodiment, the values of the terminal voltages Vu, Vv, Vwand the value of the reference voltage Vref to be compared with eachother are made different from each other through the setting of thecomparators 224, 226, 228. Each of the comparators 224, 226, 228 isconstructed as illustrated in FIG. 37.

Each comparator is so constructed that it includes a differentialamplifier circuit 240 and an output circuit 250. In the differentialamplifier circuit 240, a constant current source 241 connected to thepositive pole of the battery 214 is connected with the emitters of apair of transistors 242, 243. The bases of the pair of transistors 242,243 are respectively connected with the non-inverting input terminal (+)and the inverting input terminal (−) of the comparator 224, 226, 228.The collectors of the transistors 242, 243 are respectively connectedwith the collectors of transistors 244, 245. The bases of thetransistors 244, 245 are short-circuited to each other, and the emittersof the transistors 244, 245 are grounded through resistive elements 246,247. The bases of the transistors 244, 245 are connected to the junctionpoint between the transistor 242 and the transistor 244.

The output circuit 250 includes a transistor 252 and a transistor 254,and the base of the transistor 252 is connected to the junction pointbetween the transistor 243 and the transistor 245. The emitter of thetransistor 252 is grounded, and its collector is connected to theconstant current source 241. The base of the transistor 254 is connectedwith the collector of the transistor 252, and the emitter of thetransistor 254 is grounded. The collector of the transistor 254 isconnected with power supply obtained by stepping down the positivepotential of the battery 214 to a predetermined voltage through aresistive element 256. Further, it makes the output terminal of thecomparator 224, 226, 228.

With this construction, the following operation is performed. When thevoltage of the non-inverting input terminal is higher than the voltageof the inverting input terminal, the transistor 243 is turned on and thetransistor 242 is turned off. Therefore, a current from the constantcurrent source 241 flows to the base of the transistor 252 through thetransistor 243. As a result, the transistor 252 is turned on and thetransistor 254 is turned off. Therefore, the output of the comparator224, 226, 228 is brought to the positive potential of the battery 214.In other words, the comparator outputs a logical H signal.

When the voltage of the non-inverting input terminal is lower than thevoltage of the inverting input terminal, the transistor 242 is turned onand the transistor 243 is turned off. As a result, a current from theconstant current source 241 flows into the bases of the transistors 244,245 through the transistor 242. For this reason, the transistors 244,245 are turned on, and no current flows to the base of the transistor252. For this reason, the transistor 252 is turned off and thetransistor 254 is turned on. Therefore, the output of the comparator224, 226, 228 is brought to ground potential. In other words, thecomparator outputs a logical L signal.

The accuracy of comparison of a pair of input signals with respect tomagnitude by the differential amplifier circuit 240 depends on thesymmetry of pairs of elements in the differential amplifier circuit 240respectively corresponding to the input terminals. The pairs of elementsinclude the transistor 242 and the transistor 243, the transistor 244and the transistor 245, and the resistive element 246 and the resistiveelement 247. Specifically, the accuracy of comparison is enhanced withenhancement of symmetry.

In this embodiment, a pair of elements respectively corresponding to theinput terminals is made asymmetrical. As a result, when the values ofvoltages applied to the non-inverting input terminal and the inputterminal are identical, the output signal of the comparator 224, 226,228 takes a certain logical value without fail. This is because, in thedifferential amplifier circuit 240, either of the transistors 242, 243is more prone to be turned on even when an identical voltage is appliedto the non-inverting input terminal and the inverting input terminal.

When the transistors 242, 243 are so structured that they areasymmetrical, for example, the following is implemented. When the amountUVF+ of voltage drop between emitter and collector due to the transistor242 being turned on is larger than the amount UVF− between emitter andcollector due to the transistor 243 being turned on, the transistor 243is more prone to be turned on. When the transistors 244, 245 are sostructured that they are asymmetrical, the following is implemented.When the amount UVf+ of voltage drop between emitter and collector dueto the transistor 244 being turned on is larger than the amount UVf− ofvoltage drop between emitter and collector due to the transistor 245being turned on, the transistor 243 is more prone to be turned on. Whenthe resistance value of the resistive element 246 is higher than theresistance value of the resistive element 247, the transistor 243 ismore prone to be turned on.

With this setting, the following is implemented. In a situation in whichthe reference voltage Vref and the terminal voltages Vu, Vv, Vw agreewith each other, the comparators 224, 226, 228 can be caused todetermine that either is higher without fail. For this reason, even inthe situation illustrated in FIG. 36A, it can be avoided that the outputvalues of the comparators 224, 226, 228 are frequently inverted. Toaccurately bring an interval between zero-crossing times intocorrespondence with an interval of 60°, it is desirable to take thefollowing measure. In a situation in which the true value of thereference voltage Vref and the true values of the terminal voltages Vu,Vv, Vw agree with each other, the results of comparison by thecomparators 224, 226, 228 with respect to which is higher, the terminalvoltages Vu, Vv, Vw or the terminal voltage, are made identical.Further, it is desirable to make the difference between the referencevoltage Vref and the terminal voltage Vu, Vv, Vw when the output of thecomparator 224, 226, 228 is inverted identical for all the phases. Inthis embodiment, for this purpose, the comparators 224, 226, 228 aremade identical with one another in structure.

According to this embodiment, the following advantages can be providedin addition to the advantages of the ninth embodiment.

(7) Pairs of elements in the differential amplifier circuits 240respectively corresponding to the pairs of input terminals of thecomparators 224, 226, 228 are so structured that they are asymmetrical.Thus, the relative magnitude relation between a pair of input signals tobe compared with each other can be shifted. For this reason, thefollowing can be implemented in such a situation that the rotationalspeed of the brushless motor 2 is substantially zeroed and thus thereference voltage Vref and the terminal voltages Vu, Vv, Vw become equalto each other. The relative difference between these values to becompared with each other can be expanded.

(8) The comparators 224, 226, 228 are made identical in structure forall the phases. Thus, the intervals between zero-crossing times can beaccurately set to 60°.

In the tenth embodiment, the circuitry of the comparators 224, 226, 228may be so constructed that they include MOS transistors.

In both ninth and tenth embodiments, the following medications may bemade.

The specified time point setting counter and the measuring counter maybe made identical in count speed, and the initial value of the specifiedtime point setting counter is set according to the value of the counterbefore initialization (maximum value). When the specified time point isset to a time point delayed by 30° from the zero-crossing time point,for example, ½ of the maximum value of the measuring counter is taken asthe initial value of the specified time point setting counter. Themasking period counter and the measuring counter may be made identicalin count speed, and the initial value of the masking period counter isset according to the value of the counter before initialization (maximumvalue). When an angular range from the zero-crossing time point to 45°is set as the masking period, ¾ of the maximum value of the counter istaken as the initial value of the masking period counter. In place ofthe virtual neutral point voltage, the neutral point voltage of thebrushless motor 2 may be used for the reference voltage Vref. Theswitching elements SW1, SW3, SW5 on the high side of the respective armsmay be constructed of an N-channel MOS transistor. The power supplyconnected with the brushless motor 2 need not be the battery 214 but maybe a generator. The brushless motor 2 need not be an actuator of anin-vehicle fuel pump, but may be an actuator of an in-vehicle coolingfan. The rotary machine need not be a three-phase brushless motor, butmay be a motor of any number of phases. Further, it need not be a motorbut may be a generator.

Eleventh Embodiment

In an eleventh embodiment, a rotary machine driving apparatus isconstructed as shown in FIG. 38 in the similar manner as in the sixthembodiment (FIG. 18) and the ninth embodiment (FIG. 31). In thisembodiment, however, a current detector 228 is provided in place of thevoltage detector 225 (FIG. 18). Thus, currents passed through theswitching elements SW1 to SW6 are detected based on their onresistances. That is, the current detector 228 includes detectiontransistors for detecting the currents respectively passed through theswitching elements SW1 to SW6. The sources of the switching elements SW1to SW6 and the corresponding detection transistors are short-circuitedtogether and their gates are short-circuited together, and currentmirror circuits are thereby constructed. Thus, the currents passedthrough the switching elements SW1 to SW6 can be detected based on theoutput currents of the detection transistors. In actuality, it isdesirable that the current detector 228 should be formed in proximity tothe inverter 12. For information, a technique for constructing a currentmirror circuit to detect a current is disclosed in, for example,JP-A-10-256541.

The switching controller 227 turns on and off the switching elements SW1to SW6 through the driver 222. In this example, it basically carries outswitching control by a 120°-energization method. More specifically, avirtual neutral point voltage (reference voltage Vref) is obtained as aresult of voltage division by resistive elements RU, RV, RW with respectto the terminal voltages Vu, Vv, Vw of the respective phases of thebrushless motor 2. Based on time point with which this virtual neutralpoint voltage agrees with the terminal voltage Vu, Vv, Vw of each phaseof the brushless motor 2, time point (zero-crossing time point) withwhich an induced voltage agrees with the reference voltage Vref isdetected. Then, it changes the operation of the switching elements SW1to SW6 with time point (specified time point) delayed from thezero-crossing time point by a predetermined electrical angle (e.g.,30°). When the current detected by the current detector 228 exceeds acurrent limit value, however, the following measure is taken to limitthe current (amount of energization) passed through the brushless motor2. Instead of taking a period of 120° as a period for which theswitching elements SW2, SW4, SW6 are turned on, PWM control is carriedout during this period.

The switching controller 227 may be constructed as a logic circuit ormay be constructed as a central processing unit and a storage unit forstoring a program.

FIG. 39 illustrates the way switching control is carried out by theswitching controller 227 in 120°-energization control. Specifically, (a)illustrates the transition of the terminal voltages Vu, Vv, Vw indicatedby solid lines and the reference voltage Vref. In this embodiment, thevirtual neutral point voltage is used for the reference voltage Vref.Though, in actuality, the reference voltage Vref fluctuates, it isconsidered to be constant here for the sake of simplicity. (b)illustrates the transition of the results of comparison of the terminalvoltages Vu, Vv, Vw with the reference voltage Vref for magnitude(comparison signals PU, PV PW). (c) illustrates the transition of alogically combined signal PS of the comparison signals PU, PV, PW. (d)illustrates the transition of a logically combined signal (expectationsignal) Se of the comparison signals PU, PV, PW expected when thezero-crossing time occurs while the switching elements SW1 to SW6 are inoperation. (e) illustrates the transition of a detection signal Qs withrespect to zero-crossing time point. This is a signal whose rising edgesand falling edges are synchronized with zero-crossing time point. (f)illustrates the transition of the values on various counters, and (g)illustrates the transition of actuating signals for the switchingelements SW1 to SW6. The actuating signals illustrated in (g) includeactuating signals U+, V+, W+ for the high side switching elements SW1,SW3, SW5 of the arms of the respective phases and actuating signals U−,VW− for the low side switching elements SW2, SW4, SW6 of the arms of therespective phases. The high side switching elements SW1, SW3, SW5 of thearms of the respective phases are P-channel transistors; therefore, theperiods for which these actuating signals U+, V+, W+ are at logical Lare the periods for which they are on.

The combined signal PS is a three-bit signal, and the respective logicalvalues of the comparison signals PU, PV, PW respectively agree with thelogical values of its highest order bit, intermediate bit, andlowest-order bit. That is, when the comparison signal PU is at logical Hthe highest-order bit is set to 1; and when the comparison signal PU isat logical L the highest-order bit is set to 0. For this reason, whenthe comparison signals PU, PV, PW are respectively at H, L, and H, forexample, the combined signal PS is set to 101 in binary notation and 5in decimal notation. In FIG. 39, both the combined signal PS and theexpectation signal are represented in decimal notation.

The solid lines in (f) indicate the value Cm of a measuring counter formeasuring a time interval between adjacent zero-crossing times. Asillustrated, the count Cm of the measuring counter is initialized eachtime the zero-crossing time occurs, and newly starts time countingoperation. A time interval between adjacent zero-crossing times hascorrelation with rotational speed. For this reason, the value Cm of thecounter immediately before it is initialized (the maximum value of thecounter) provides a parameter having correlation with rotational speed.

The one-dot chain line in (f) indicates the value Cs of a specified timepoint setting counter that counts a time required from whenzero-crossing time point occurs to when specified time point occurs andthereby sets a specified time point. The specified time point settingcounter takes the value of the counter before initialization as itsinitial value at the zero-crossing time and decrements it. Then, it setsthe time point with which the value is zeroed as a specified time point.At this time, the following operation is performed. When the intervalbetween zero-crossing time point and specified time point is 30°, forexample, the decrement speed is set to twice the increment speed of themeasuring counter. In consideration of that the time interval betweenadjacent zero-crossing times is 60°, it can be thought that this settingmakes it possible to delay the time point with which the value of thespecified time point setting counter becomes 0 by 30° from thezero-crossing time point.

The two-dot chain lines in (f) indicate the value Cmk of a maskingperiod counter. The masking period counter determines a masking periodfor which detection of the zero-crossing time based on the comparison ofthe terminal voltages Vu, Vv, Vw with the reference voltage Vref formagnitude is inhibited (disabled). This counter is for preventing thefollowing event. When the terminal voltages Vu, Vv, Vw agree with thereference voltage Vref during a period for which a current is suppliedthrough the diodes D1 to D6, the zero-crossing time is erroneouslydetected. This counter also takes the value of the counter beforeinitialization as its initial value at the zero-crossing time anddecrements it. Then, it sets the period before the value is zeroed as amasking period. When the masking period is set to a period from thezero-crossing time to 45°, for example, the decrement speed can be setto 3/2 times the increment speed of the measuring counter.

When the value of the masking period counter is zeroed, the comparisonsignals PU, PV, PW and the combined signal PS are enabled. When thecombined signal PS agrees with the expectation signal during thisperiod, the detection signal Qs is inverted. At the zero-crossing timewhen the detection signal Qs is inverted, the specified time pointsetting counter starts decrementing, and when its value is zeroed, theoperation of the switching elements SW1 to SW6 is changed.

The specified time point with which the switching elements SW1 to SW6are turned on and the zero-crossing time point have one-to-onecorrespondence with each other. For this reason, the behavior of theterminal voltages Vu, Vv, Vw of the respective phases is uniquelydetermined according to the operating state of the switching elementsSW1 to SW6. Consequently, the above expectation signal can be uniquelydetermined.

Next, processing for 120°-energization control is carried out asillustrated in FIG. 40 and FIG. 41. The processing for setting thecounter values on the above three counters is repeatedly carried out bythe drive control circuit 220, for example, in a predetermined cycle.

In this series of processing, at S310, it is checked whether or not thevalue Cmk of the masking period counter is 0. When it is determined thatthe value is zero, it is determined at S312 whether or not the combinedsignal PS of the comparison signals PU, PV, PW has varied. When it isdetermined at S312 that the combined signal PS has varied, it isdetermined at S314 whether or not the combined signal PS and theexpectation signal Se agree with each other. This processing is fordetermining whether or not change in the magnitude relation between theterminal voltages Vu, Vv, Vw and the reference voltage Vref agrees withchange assumed from the operating state of the switching elements SW1 toSW6. When it is determined that the combined signal PS and theexpectation signal Se agree with each other, it is checked whether ornot an inversion permission flag Fip is set to ON. The inversionpermission flag Fip is a flag that is set to ON when the detectionsignal Qs has not been inverted yet after the value Cmk of the maskingperiod counter was zeroed. For this reason, when the combined signal PSand the expectation signal Se agree with each other for the first timeafter the value of the masking period counter was zeroed, the inversionpermission flag Fip is set to ON.

When the inversion permission flag is set to ON, the detection signal Qsis inverted at S318. At S320, the inversion permission flag is set toOFF. At S322, subsequently, the value Cm of the measuring counter istaken as the values Cs and Cmk on the specified time point settingcounter and the masking period counter. At S324, the measuring counteris initialized (Cm=0).

When a negative determination is made at S310, the value Cm of themeasuring counter is incremented at S326. At S328, subsequently, it ischecked whether or not the value Cs of the specified time point settingcounter is zero. When the value of the specified time point settingcounter is zero, the above inversion permission counter is set to ON atS330. When the value Cs of the specified time point setting counter isnot zero, the value Cs of the specified time point setting counter isdecremented at S332.

When the processing of S330 or S332 is completed, it is determined atS334 whether or not the value Cmk of the masking period counter is zero.When the value of the masking period counter is not zero, the maskingperiod counter is decremented at S336.

When an affirmative determination is made at S334, when a negativedetermination is made at any of S312 to S316, and when the processing ofS336 is completed, this series of processing is once terminated.

The processing of FIG. 41 is for changing the operation of the switchingelements SW1 to SW6 based on the above specified time point settingcounter in 120°-energization control. This processing is repeatedlycarried out by the drive control circuit 220, for example, in apredetermined cycle.

In this processing, at S340, it is checked whether or not the value Csof the specified time point setting counter has been zeroed. Thisprocessing is for determining whether or not it is the time to changethe operation of the switching elements SW1 to SW6. When it isdetermined that the value of the specified time point setting counterhas been zeroed, the operation of the switching elements SW1 to SW6 ischanged at S342. The operation of the switching elements is changedbased on an operation pattern (switching pattern) of the switchingelements SW1 to SW6. More specifically, though the operation pattern ofthe switching elements SW1 to SW6 is changed at intervals of electricalangle of 60° as illustrated in FIG. 39, it has 360°-periodicity. Forthis reason, the next operating state of the switching elements SW1 toSW6 is uniquely determined from the present operating state.Consequently, the operation of the switching elements SW1 to SW6 ischanged based on this unique relation.

At S344, subsequently, the expectation signal Se is updated. When theoperating state of the switching elements SW1 to SW6 changes, it ispresumed that one zero-crossing time occurs during a period for whichthis operating state is maintained. The values of the comparison signalsPU, PV, PW at this zero-crossing time are uniquely determined from theoperating state. For this reason, the expectation signal Se is updatedto a value corresponding to the present operating state. Specifically,the following processing is carried out. If the previous expectationsignal is 1, the present expectation signal is set to 5; if the previousexpectation signal is 5, the present expectation signal is set to 4; ifthe previous expectation signal is 4, the present expectation signal isset to 6; if the previous expectation signal is 6, the presentexpectation signal is set to 2; if the previous expectation signal is 2,the present expectation signal is set to 3; and if the previousexpectation signal is 3, the present expectation signal is set to 1.

When a negative determination is made at S340 and when the processing ofS444 is completed, this series of processing is once terminated.

According to the above processing, 120°-energization control can beappropriately carried out.

FIG. 42 illustrates processing in the above PWM control. This processingis repeatedly carried out by the drive control circuit 220, for example,in a predetermined cycle.

In this processing, at S350, it is determined by the current detector228 illustrated in FIG. 38 whether or not the maximum value of currentsImax passed through the individual phases of the brushless motor 2exceeds a threshold value Iref. This threshold value Iref can be set,for example, based on the maximum value of currents permitted in theswitching elements SW1 to SW6. When it is determined that the thresholdvalue is exceeded, PWM processing is carried at S352. In thisprocessing, the low side switching elements SW2, SW4, SW6 of the arms ofthe inverter 12 are repeatedly turned on and off during an ON period(On-permitted period) determined by the above specified time point. Whena negative determination is made at S350 and when the processing of S352is completed, this series of processing is once terminated.

When the above PWM control is carried out, the terminal voltages Vu, Vv,Vw frequently vary. According to the processing illustrated in FIG. 40,however, zero-crossing time point can be detected with accuracy even inthis case. FIG. 43 illustrates the way switching control is carried outin PWM control. (a) to (e) in FIG. 43 correspond to (a) to (e) in FIG.39, respectively.

This figure illustrates the way PWM control is carried out during an ONoperation-permitted period for the low side switching element SW2 of theU-phase arm (a period for which it is on in 120°-energization control).As illustrated, the U-phase terminal voltage Vu rises and becomes higherthan the positive voltage VB of the battery 214 each time the switchingelement SW2 is switched from ON state to OFF state. This is because,when the switching element SW2 is switched from ON state to OFF state, avoltage that will keep the current supplied to the U-phase when it wasON, passed is produced by the inductance component of the brushlessmotor 2. At this time, the switching elements SW1, SW2 of the U-phaseare both OFF; therefore, a current is supplied through the U-phasethrough the diode D1. For this reason, the U-phase terminal voltage Vubecomes higher than the positive voltage VB of the battery 214approximately by an amount equivalent to voltage drop in the diode D1.

Since the switching elements SW5, SW6 of the W-phase are both OFF atthis time, the W-phase is brought to a high-impedance state. The W-phaseterminal voltage Vw at this time is pulled up by the V-phase terminalvoltage Vv and the U-phase terminal voltage Vu that have become equal tothe positive voltage VB of the battery 214 as a result of the switchingelement SW3 being turned on. Therefore, it becomes higher than thepositive voltage VB of the battery 214. For this reason, the referencevoltage Vref set by the virtual neutral point also becomes higher thanthe positive voltage VB of the battery 214 each time the switchingelement SW2 is turned off. Though the reference voltage Vref is lowerthan the U-phase terminal voltage Vu when the switching element SW2 isturned off, it is higher than the W-phase terminal voltage Vw at thattime. For this reason, the W-phase terminal voltage Vw is kept lowerthan the reference voltage Vref until the W-phase induced voltagebecomes equal to or higher than the reference voltage Vref.

Thus, the comparison signal PW is brought to logical H for the firsttime when the zero-crossing time occurs. As illustrated in FIG. 40,therefore, the change time point of the detection signal Qs and thezero-crossing time point can be brought into one-to-one correspondencewith each other by taking the following measure. The detection signal Qsis inverted when the combined signal PS agrees with the expectationsignal for the first time. When the switching element SW2 is turned off,the W-phase terminal voltage Vw can alternately take a value higher thanand a value lower than the reference voltage Vref. Even in this case, atime when the combined signal PS and the expectation signal agree witheach other for the first time can be taken as the zero-crossing time.This is because in this case, only the following takes place. Thecombined signal of 4 in the figure is replaced with 5.

Meanwhile, when a one-bit combined signal is generated from thecomparison signals PU, PV, PW as illustrated in FIG. 12, the combinedsignal is frequently inverted in PWM control. Therefore, zero-crossingtime point cannot be detected.

In reality, the comparison signal PW may be instantaneously brought tological H before the zero-crossing time occurs because of ringing noisein conjunction with change of the operation of the switching elementsSW1 to SW6. In this case, however, the logical value of the comparisonsignal PU is likely to differ from that indicated in FIG. 43. Therefore,the possibility that the three-bit combined signal PS and theexpectation signal agree with each other before the zero-crossing timeoccurs is minimized.

To more reliably avoid the erroneous detection of zero-crossing timepoint due to the influence of ringing noise, it is desirable to take thefollowing measure. Of the values of the combined signal PS, those whoseduration is equal to or shorter than a predetermined value are notcompared with the expectation signal. This processing can beaccomplished, for example, by taking the following measure. The combinedsignal PS is sampled with a high-speed sampling period, and values thatdiffer twice or more in adjacent sampling periods are considered to beinfluenced by noise and excluded. The above erroneous detection can alsobe more reliably avoided by slightly offset correcting the referencevoltage Vref generated based on the virtual neutral point.

According to this embodiment described in detail, the followingadvantages can be provided.

(1) The combined signal (expectation signal Se) of the comparisonsignals PU, PV, PW assumed when the zero-crossing time occurs in thepresent operating state of the switching elements SW1 to SW6 is comparedwith the actual combined signal PS with respect to each phase. Based onthe results of these comparisons, information pertaining to theelectrical angle of the brushless motor 2 is acquired. Thus, moreelaborate information can be used as compared with cases where a one-bitcombined signal of the comparison signals PU, PV, PW is used. For thisreason, highly accurate information can be acquired with respect toelectrical angle.

(2) Zero-crossing time point is detected based on agreement between theassumed values of the comparison signals PU, PV, PW and the actualvalues with respect to all the phases. In other words, zero-crossingtime point is detected based on agreement between the three-bit combinedsignal PS and the expectation signal with respect to all the bits. Thus,conditions for detecting zero-crossing time point can be made stricteras compared with cases where a time when a one-bit combined signalindicating the results of comparison with respect to all the phasesvaries is taken as the zero-crossing time. For this reason,zero-crossing time point can be detected with accuracy.

(3) A specified time point that provides a basis for changing theoperating state of the switching elements SW1 to SW6 is set based onzero-crossing time point. Thus, a specified time point can beappropriately set.

(4) Specified time point and zero-crossing time point are brought intoone-to-one correspondence with each other. As a result, the operatingstate of the switching elements SW1 to SW6 is also brought intoone-to-one correspondence with the zero-crossing time point. Therefore,the comparison signals PU, PV, PW (expectation signal) assumed when thezero-crossing time occurs in the present operating state of theswitching elements SW1 to SW6 can be uniquely determined.

(5) The reference voltage Vref is set by the virtual neutral pointvoltage of the brushless motor 2. When a current supplied to thebrushless motor 2 is excessively large, PWM control is carried out inthe respective ON operation-permitted periods for the switching elementsSW2, SW4, SW6, determined by the specified time point, and operation isswitched between ON operation and OFF operation. In this case,zero-crossing time point cannot be detected by a one-bit logicallycombined signal of the comparison signals PU, PV, PW. According to thisembodiment, meanwhile, zero-crossing time point can be determined withaccuracy based on comparison of the expectation signal with the combinedsignal PS, both of which are three-bit signals.

In the eleventh embodiment, zero-crossing timing is detected based onagreement between the combined signal PS and the expectation signal Sewith respect to all the bits. However, for example, zero-crossing timepoint may be detected based on agreement between bits corresponding to aphase in which the induced voltage and the reference voltage Vrefzero-cross each other in the PWM control.

Twelfth Embodiment

A twelfth embodiment is similar to the ninth embodiment (FIG. 31 to FIG.36).

If the battery 214 and the inverter 12 are insufficiently connectedresulting in electrical disconnection therebetween or any other likeevent occurs, the following phenomenon can take place. Because oftransmission of vibration of the vehicle to the battery 214 or any otherlike reason, the battery 214 and the inverter 12 may be instantaneouslydisconnected from each other and then conduction is established betweenthem again. If power supply to the brushless motor 2 is temporarilyinterrupted at this time, the rotational speed of the brushless motor 2is reduced. If fuel discharged from a fuel tank to the upstream side bya fuel pump flows back at this time, force on the reverse rotation sideis exerted on the brushless motor 2 and this can eventually causereverse rotation. If, in this situation, the switching elements SW1 toSW6 are operated as under normal conditions, an oscillation phenomenonthat the brushless motor 2 repeats normal rotation and reverse rotationoccurs. It is difficult to control the brushless motor 2 in a properrotating state.

That the brushless motor 2 is rotating in reverse can be appropriatelydetected based on the above combined signal PS composed of three bits.More specifically, as illustrated in FIG. 44, when the brushless motor 2rotates normally (in the forward direction), time-series data on thecombined signal PS should agree with time-series data on the expectationsignal Se. When the brushless motor 2 is rotating, meanwhile,time-series data on the combined signal PS should agree with dataobtained by time-reversing time-series data on the expectation signal asillustrated in FIG. 45. For this reason, reverse rotation of thebrushless motor 2 can be detected based on the combined signal PS.

It is possible that, when the rotating state of the brushless motor 2becomes abnormal, all the switching elements SW1 to SW6 are turned offand the operation waits until the brushless motor 2 stops. Then, thebrushless motor is restarted. In this case, however, it takes a longtime to restore the brushless motor 2 to a normal state.

To cope with this, the following processing is carried out in thisembodiment. When it is detected that the brushless motor 2 rotates inreverse, processing is carried out to forcibly stop the rotation of thebrushless motor 2 and then restart processing is carried out. FIG. 46illustrates processing for restarting the brushless motor 2 in thisembodiment. This processing is repeatedly carried out by the drivecontrol circuit 220, for example, in a predetermined cycle.

This series of processing is carried out as follows. At S360, it ischecked whether or not the value Cmk of the masking period counter iszero. When it is determined that the value of the masking period counteris zero, it is determined at S362 whether or not the combined signal PSof the comparison signals PU, PV, PW has changed. This processing is fordetermining whether or not it is the zero-crossing time. When it isdetermined that the combined signal PS has changed, it is determined atS364 whether or not the present combined signal agrees with theexpectation signal before the last. This processing is for determiningwhether or not the brushless motor 2 is rotating in reverse. Morespecifically, as illustrated in FIG. 44 and FIG. 45, when the brushlessmotor 2 is rotating in reverse, time-series data on the combined signalPS is reversed. Therefore, it is presumed that the present combinedsignal PS agrees with the expectation signal before the last. When thepresent combined signal PS agrees with the expectation signal Se beforethe last, it is determined at S66 that the brushless motor 2 is rotatingin reverse.

At S368, subsequently, processing is carried out to forcibly stop therotation of the brushless motor 2. Specifically, the switching elementsSW1, SW3, SW5 or the switching elements SW2, SW4, SW6 are all turned onto short-circuit all the phases of the brushless motor 2. Thus, acurrent is supplied through the brushless motor 2 only by an inducedvoltage produced in conjunction with the rotation of the brushless motor2. This current is quickly attenuated by the resistance of the currentpassage and the like. As a result, the rotational energy of thebrushless motor 2 is converted into electrical energy and thenattenuated. For this reason, the brushless motor 2 can be quicklystopped.

When the rotational speed of the brushless motor 2 is substantiallyzeroed (S370: YES), restart processing is carried out at S372. Therotational speed of the brushless motor 2 is calculated based on timeintervals between adjacent zero-crossing time points. This can be doneby using the maximum value of Cm of the measuring counter.

When a negative determination is made at any of S360 to S364 or when theprocessing of S372 is completed, this series of processing is onceterminated.

According to this embodiment, the following advantages can be providedin addition to the advantages (1) to (5) of the eleventh embodiment.

(6) The rotating state of the brushless motor 2 is determined to beabnormal based on disagreement between the combined signal PS assumedwhen the zero-crossing time occurs in the present operating state of theswitching elements SW1 to SW6 and the expectation signal. The use of thethree-bit combined signal PS and the three-bit expectation signal Semakes it possible to appropriately determine the presence or absence ofan abnormality.

(7) The presence of an abnormality that the brushless motor 2 rotates inreverse is determined based on agreement between what is obtained bytime-reversing the time-series pattern of the combined signal PS assumedfrom the time-series pattern of the operating state of the switchingelements SW1 to SW6 and the actual time-series pattern. Thus, that thebrushless motor 2 is rotating in reverse can be appropriately detected.

(8) When it is determined that the brushless motor 2 is rotating inreverse, processing is carried out to forcibly stop the brushless motor2 and thereafter the brushless motor 2 is restarted. Thus, the brushlessmotor 2 can be quickly restored to normal state.

(9) Conduction is established from all the phases of the brushless motor2 to either the positive pole or the negative pole of the battery 214 toforcibly stop the brushless motor 2. Thus, the rotational energy of thebrushless motor 2 can be quickly reduced.

In the twelfth embodiment, all the phases of the brushless motor 2 areshort-circuited to forcibly stop the brushless motor 2. Instead,switching of the switching elements SW1 to SW6 may be controlled so asto generate torque for stopping the rotation. Further, the reverserotation is detected on condition that the combined signal PS agreeswith the expectation signal before the last. Reverse rotation may bedetected when the next combined signal PS agrees with the expectationsignal preceding the expectation signal before the last, in addition tothis condition.

Thirteenth Embodiment

A third embodiment is directed to improve the following problem. Thatis, when any of phase lines of the brushless motor 2 is disconnected,the inverter 12 supplies a voltage to the lines of the motor 2 which arenot disconnected. However, it is likely that flow of the current will beimpaired and an excessive load will be exerted on the brushless motor 2.It is therefore proposed by JP 2-290191A to determine whether a phasecurrent flows by using a shunt resistor and detect presence/absence ofdisconnection based on this determination. In this instance, however, asensing element is necessitated to sense a voltage drop at the shuntresistor. This will increase the size of the circuit of the drivecontrol circuit 220.

According to this embodiment, therefore, the presence/absence ofdisconnection is detected based on the comparison signals PU, PV, PW.Since those comparison signals PU, PV, PW are taken in by the controlcircuit 220 to be used to operate the switching elements SW1 to SW6.Therefore, by detecting the disconnection based on those signals,increase of the size of the circuit can be avoided. The principle ofdetecting the disconnection based on the comparison signals PU, PV, PWis described first.

As described above, the comparison signals PU, PV PW changes asillustrated in (b) of FIG. 43. Here, since the reference voltage Vrefexceeds the positive pole voltage VB of the battery 214, when theswitching elements, which are PWM-controlled, are switched from ON toOFF. As a result, the comparison signal of a phase in which theswitching element is continue to be ON is reversed in logic value. Ifthe brushless motor 2 is in the disconnected condition, as illustratedin FIG. 47, the comparison signal is not reversed in logic value. Here,(a) and (b) of FIG. 47 correspond to (a) and (b) of FIG. 43, andillustrate a case, in which the phase line of W-phase of the brushlessmotor 2 is disconnected at a side closer to the brushless motor 2 than ajunction with the resistive element RW.

As illustrated in FIG. 47, the terminal voltage Vw of the W-phase fallsto about the negative pole voltage of the battery 214. This is because,although the W-phase is in the high impedance state in the exampleillustrated in FIG. 47, the potential in the W-phase is decreased towardthe negative potential of the battery 214 due to parasitic capacitancebetween the gate and the drain of the switching element SW6 and thelike. In this case, when the switching element SW2 is switched from OFFto ON, current flows in the diode D1. As a result, the terminal voltageVu of the U-phase increases above the positive pole voltage VB of thebattery 214, but the reference voltage Vref falls below the positivepole voltage VB of the battery 214. This is because the terminal voltageof the W-phase is decreased by the disconnection.

For this reason, irrespective of the condition of the switching elementSW2, the reference voltage Vref continues to be lower than the terminalvoltage Vu of the V-phase connected to a side of the positive polevoltage VB of the battery 214. Thus, as illustrated in (b) of FIG. 47,the comparison signal PV of the V-phase continues to be H and isdifferent from the state illustrated in (b) of FIG. 43. Therefore, thedisconnection of the brushless motor 2 can be detected based on thedifference between these states.

Although FIG. 47 illustrates a case where disconnection occurs in aphase (to be changed to the high impedance) in which the switchingelements in both the high side arm and the low side arm are turned off.The disconnection can be detected in the similar manner by using thecomparison signal PV even when a phase (U-phase in FIG. 47) which isPWM-controlled is disconnected. This is because, since the terminalvoltage Vu of the U-phase of the battery 214 continues to be thenegative pole voltage of the battery 214, the reference voltage Vrefdoes not exceed the positive pole voltage VB of the battery 214.

FIG. 48 illustrates processing of detecting disconnection. Thisprocessing is carried out repeatedly by the control circuit 220, forexample, in a predetermined period.

In a series of this processing, at S380, it is checked whether the PWMcontrol, which is carried out at S352 in FIG. 42, is being carried out.If it is determined that the PWM control is being carried out, a phase,which is in the ON operation-permitted period among the switchingelements SW1, SW3, SW5 in the high side arm, is specified at S382. Bythis step, the V-phase is specified in the example of FIG. 47. At asubsequent S384, it is checked whether it is in the ONoperation-permitted period of the specified phase. This step is forspecifying a period in which the terminal voltage of the appropriatephase to be used for detecting disconnection does not change.

If it is determined that it is in the ON operation-permitted period atS384, it is further checked at S386 whether the logical value of thecomparison signal of the phase specified at step S82 is L. This step isfor determining the presence/absence of disconnection. If it isdetermined affirmatively at step S386, a L detection flag is set to onat S388 to indicate that the logical value has become L. This step maybe carried out as a step for changing a register value in the controlcircuit 220.

When S388 has been completed or negative determination has been made atS386, the processing returns to S390. In S390, it is checked whether theL detection flag is on or not. This step is for determining thepresence/absence of the disconnection. That is, if the logic value ofthe comparison signal does not become L within the on-permitted periodof the phase specified at S382, it is so considered that the phenomenonindicated by (b) of FIG. 47 has occurred. In this instance, it can bedetermined that the disconnection has occurred. Therefore, if a negativedetermination is made at S390, a notification of detection ofdisconnection is issued from the control apparatus to an external sideat step S392. When S392 has been completed or negative determination hasbeen made at step S380 or S390, the L detection flag is set to off atS394.

When S394 has been completed, the series of processing is terminated.

According to this embodiment, the following advantages are obtained inaddition to the advantages of the eleventh embodiment.

(10) Under the condition that only one phase of the brushless motor 2 ismade conductive to the negative pole terminal of the battery 214 andanother one phase is made conductive to the positive pole terminal ofthe battery 214, presence/absence of the disconnection of the brushlessmotor 2 is detected based on the presence/absence of inversion of thecomparison signal of the another one phase at the time of turning offthe switching element which makes the negative pole terminal and thebrushless motor 2 conductive. Thus, disconnection of the brushless motor2 can be detected.

(11) In the 120°-energization control, the reference voltage Vref doesnot exceed the positive pole voltage of the battery 214. In thisinstance, since the disconnection cannot be detected based on thecomparison signal, the disconnection is detected in the PWM control.Therefore, detection of disconnection can be attained appropriately.

Fourteenth Embodiment

A fourteenth embodiment is illustrated in FIG. 49. The brushless motor 2is a two-phase motor. For detecting presence/absence of disconnection inthe two-phase motor 2 in the similar manner as in the thirteenthembodiment, a series connection of diodes D5, D6 is connected inparallel to a series connection of the switching elements SW1, SW2 and aseries connection of the switching elements SW3, SW4. A junction betweenthe diodes D5, D6 is connected to the neutral point of the brushlessmotor 2 a. Thus, a phase connected to a junction between the switchingelements SW1, SW2 is defined to be a U-phase, a phase connected to ajunction between the switching elements SW3, SW4 is defined to be aV-phase, and a phase connected to the junction between the diodes D5, D6is defined to be a W-phase.

A comparator Cu produces a comparison signal PU by comparing theterminal voltage Vu and the reference voltage Vref. A comparator Cvproduces a comparison signal PV by comparing the terminal voltage Vv andthe reference voltage Vref. A comparator Cw produces a comparison signalPW by comparing the terminal voltage Vw with the reference voltage Vref.Based on these comparison signals PU, PV, PW, the disconnection can bedetected in the similar manner as in the thirteenth embodiment.

The eleventh to fourteenth embodiments may be modified as describedbelow.

The specified time point is set by adjusting the decrement speed of thespecified time point setting counter relative to the increment speed ofthe measuring counter. However, these counters may be made identical incount speed, and the initial value on the specified time point settingcounter may be set according to the value on the measuring counterbefore initialization (maximum value). When the specified time point isset to a time point delayed by 30° from zero-crossing time point, forexample, ½ of the maximum value of the measuring counter may be taken asthe initial value of the specified time point setting counter.

The masking period is set by adjusting the decrement speed of themasking period counter relative to the increment speed of the measuringcounter. However, these counters may be made identical in count speed,and the initial value on the masking period counter is set according tothe value of the measuring counter before initialization (maximumvalue). When an angular range from a zero-crossing time to 45° is set asthe masking period, ¾ of the maximum value of the measuring counter maybe taken as the initial value on the masking period counter.

The abnormality in the rotating state of the brushless motor 2 is notlimited to the reverse rotation. It is essential only that, when thecombined signal PS disagrees with the expectation signal, the rotatingstate is determined to be abnormal.

The PWM control is carried out when the phase current of the brushlessmotor 2 exceeds the threshold value. However, it is also possible, forinstance, to forcibly turn off the switching element of the low sidearm, which is in the ON-permitted period, only when the currentcontinues to exceed the threshold value. An operation means forrepeating tuning on and off of the switching element in the ON-permittedperiod can thus be provided by this control.

The operation means is not limited to a means that operates theswitching elements of the low side arm, but may be a means that operatesthe switching elements of the high side arm. In this instance, in thethirteenth and fourteenth embodiments, the presence/absence ofdisconnection is detected based on the presence/absence of inversion ofthe comparison signal of the phase in which the switching element of thelow side arm may be fixed to the ON state.

The reference voltage Vref need not be the virtual neutral point, whichis formed based on the terminal voltages Vu, Vv, Vw, but may be theneutral point voltage of the brushless motor 2. Even in this case, thesame advantages as those according to the eleventh embodiment can beprovided. Even when ½ of the voltage of the battery 214 is used for thereference voltage Vref, the following can be implemented using thethree-bit combined signal and the three-bit expectation signal. Anabnormality in the rotating state can be detected with accuracy and theaccuracy of detection of zero-crossing time point can be enhanced in120°-energization control. When a phase line, which is at a side of theinverter 12 than a side of a junction with the resistive elements RU,RV, RW of the phase lines of the brushless motor 2, disconnection can bedetected by using the reference voltage Vref as the neutral voltagebased on the same phenomenon as the thirteenth embodiment.

The switching elements SW1, SW3, SW5 on the high side of the respectivearms may be constructed of an N-channel MOS transistor. The power supplyconnected with the brushless motor 2 need not be a battery 214 but maybe a generator. The brushless motor 2 need not be an actuator of anin-vehicle fuel pump, but may be an actuator of an in-vehicle coolingfan.

The multi-phase rotary machine need not be a three-phase brushlessmotor, and may be a motor of any number of phases. Further, it need notbe a motor and may be a generator. Even when the number of phases of therotary machine is changed to N (>3) in the thirteenth embodiment,disconnection can be detected in the PWM control in the same manner asin the thirteenth embodiment as long as the switching element of onlyone phase in the low side arm is in the ON-permitted period. That is,when the switching element of the only one phase is changed from ON toOFF, the reference voltage Vref becomes about (N−1)×VB/(N+Vf). Unlessthe phase number N becomes excessively large, the reference voltage Vrefremains lower than the positive pole voltage VB of the battery 214. Onthe contrary, when no disconnection occurs, the reference voltage Vrefbecomes higher than the positive pole voltage VB of the battery 214. Asa result, the disconnection can be detected based on thepresence/absence of inversion in logical value of the comparison signalof a phase corresponding to a switching element, which is fixed to theON state, of the high side arm.

Fifteenth Embodiment

A fifteenth embodiment illustrated in FIG. 51 is constructed to have abrushless motor 2, an inverter 12 and a drive control circuit 220. Thisconstruction is similar to the eleventh embodiment illustrated in FIG.38, and hence no detailed description is made.

FIG. 52 illustrates the way switching control is carried out by theswitching controller 227 in 120°-energization control. Specifically, (a)illustrates the transition of the U-phase terminal voltage Vu indicatedby a solid line, the transition of the U-phase induced voltage indicatedby a two-dot chain line, and the reference voltage Vref indicated by aone-dot chain line. (b) illustrates the transition of a signal(zero-crossing detection signal) Un related to detection ofzero-crossing time point. (c) illustrates the transition of an actuatingsignal for the switching element SW1, and (d) illustrates the transitionof an actuating signal for the switching element SW2. The modes forV-phase and W-phase switching control are the same as that for U-phaseswitching control, and the explanation and description of them will beomitted.

As illustrated in FIG. 2, the terminal voltage Vu agrees with thepositive potential or the negative potential of the battery 214 when theswitching element SW1, SW2 is ON. Meanwhile, in periods (induced voltageexposed periods) during which both the switching element SW1 and theswitching element SW2 are OFF, a period during which a current is notpassed through the U-phase exists. In these periods, the terminalvoltage Vu is equal to the induced voltage. Even in the periods duringwhich both the switching element SW1 and the switching element SW2 areOFF, the terminal voltage Vu disagrees with the induced voltage when acurrent is supplied through the diodes D1, D2 (commutation transientstate).

For this reason, the time point with which the terminal voltage Vu andthe reference voltage Vref agree with each other in the following periodis the zero-crossing time point with which the induced voltage Vu andthe reference voltage Vref agree with each other: a period during whichboth the switching element SW1 and the switching element SW2 are OFF anda current is not passed through the diode D1 or D2. For this reason, thetime point delayed from the zero-crossing time point by a predeterminedelectrical angle (e.g., 30°) is defined as the specified time point, andthis specified time point is taken as a time point with which theoperation of the switching elements SW1, SW2 is changed from OFFoperation to ON operation. The ON state is continued for a period of120° from an occurrence of the specified time point. Specifically, thefollowing specified time point is taken as the time point for switchingon the switching element SW1 of the high side arm: specified time pointdelayed by a predetermined electrical angle (e.g., 30°) from thezero-crossing time point with which the induced voltage agrees with thereference voltage Vref in its rising process. The following specifiedtime point is taken as the time point for switching on the switchingelement SW2 of the low side arm: the specified time point delayed by apredetermined electrical angle (e.g., 30°) from the zero-crossing timepoint with which the induced voltage agrees with the reference voltageVref in its falling process. The time point for switching on the U-phaseswitching elements SW1, SW2 can be determined by the zero-crossing timepoint in the rising process of the U-phase induced voltage and thezero-crossing time point in its falling process. In this embodiment, forthis reason, the zero-crossing detection signal Un that rises with thezero-crossing time point in the rising process and falls with thezero-crossing time point in the falling process is generated. Its risingedges and falling edges are utilized to set a specified time point.

FIG. 53 illustrates the way switching control is carried out in a normalcondition in which the rotational speed of the brushless motor 2 isstabilized. Specifically, (a) illustrates the transition of the terminalvoltages Vu, Vv, Vw; (b) illustrates the transition of comparisonsignals Uc, Vc, Wc indicating the magnitude relation between theterminal voltages and the reference voltage Vref; (c) illustrates thetransition of the zero-crossing detection signals Un, Vn, Wn; (d)illustrates the transition of the values on various counters; and (e)illustrates the transition of the actuating signals for the switchingelements SW1 to SW6. The actuating signals illustrated in (e) includeactuating signals U+, V+, W+ for the switching elements SW1, SW3, SW5 ofthe high side arms and actuating signals U−, VW− for the switchingelements SW2, SW4, SW6 of the low side arms. The switching elements SW1,SW3, SW5 of the high side arms are P-channel transistors; therefore, theperiods for which these actuating signals U+, V+, W+ are at logical Lare the periods for which they are ON.

The solid lines in (d) indicate the value Cm of a measuring counter formeasuring a time interval between adjacent occurrences of zero-crossingtime point. As illustrated, the measuring counter value is initializedeach time the zero-crossing time point occurs, and newly starts timecounting operation. A time interval between adjacent occurrences ofzero-crossing time point has correlation with a rotational speed. Forthis reason, the value of the counter immediately before it isinitialized (the maximum value of the counter) provides a parameterhaving correlation with rotational speed.

The one-dot chain lines in (d) indicate the value Cs of a specified timepoint setting counter that counts a time required from when thezero-crossing time point occurs to when specified time point occurs andthereby sets a specified time point. The specified time point settingcounter takes the value of the counter before initialization as itsinitial value at an occurrence of zero-crossing time point anddecrements it. Then, it sets the time point with which the value iszeroed as a specified time point. At this time, the following operationis performed. When the interval between zero-crossing time point andspecified time point is 30°, for example, the decrement speed is set totwice the increment speed of the measuring counter. This is because theintervals between adjacent occurrences of zero-crossing time point are60°. For this reason, when the rotational speed is constant, the timepoint with which the value of the specified time point setting counterbecomes 0 should be equal to time point delayed by 30° fromzero-crossing time point.

The two-dot chain lines in (d) indicate the value Cmk of a maskingperiod counter. The masking period counter determines a period (maskingperiod) for which detection of the zero-crossing time point based on thecomparison of the terminal voltages Vu, Vv, Vw with the referencevoltage Vref for magnitude is inhibited (disabled). This counter is forpreventing the following event. When the terminal voltages Vu, Vv, Vwagree with the reference voltage Vref during a period for which acurrent is supplied through the diodes D1 to D6, an occurrence ofzero-crossing time point is erroneously detected. This counter alsotakes the value of the counter before initialization as its initialvalue at an occurrence of zero-crossing time point and decrements it.Then, it sets the period before the value is zeroed as a masking period.When the masking period is set to a period from an occurrence ofzero-crossing time point to 45°, for example, the decrement speed is setto 3/2 times the increment speed of the measuring counter.

The processing of switching control is described with reference to FIG.54 and FIG. 55. FIG. 54 illustrates processing for setting the countervalues on the above three counters. This processing is repeatedlycarried out by the drive control circuit 220, for example, in apredetermined cycle.

This series of processing is carried out as follows. At S410, it ischecked whether or not the value Cmk of the masking period counter is 0.When it is determined that the value is zero, it is determined at S412whether or not any of the comparison signals Uc, Vc, Wc has beeninverted. In actuality, this processing is for determining whether theabove zero-crossing detection signal Un, Vn, Wn is at its rising edge orits falling edge. When it is determined at S412 that any signal has beeninverted, the value Cm of the counter is taken as the values Cs and Cmkof the specified time point setting counter and the masking periodcounter at S414. At S416, the measuring counter is initialized (Cm=0).

When a negative determination is made at S410 or S412, the measuringcounter is incremented at 5418. At S420, subsequently, it is checkedwhether or not the value Cs of the specified time point setting counteris zero. When the value of the specified time point setting counter isnot zero, the specified time point setting counter is decremented atS422. Meanwhile, when an affirmative determination is made at S420 orwhen the processing of S422 is completed, it is determined at S424whether or not the value of the masking period counter is zero. When thevalue of the masking period counter is not zero, the masking periodcounter is decremented at S426.

When an affirmative determination is made at S424 or when the processingof S416 or S426 is completed, this series of processing is onceterminated.

FIG. 5 illustrates flow of processing for switching on the switchingelements SW1 to SW6. This processing is repeatedly carried out by thedrive control circuit 220, for example, in a predetermined cycle.

The series of processing illustrated in FIG. 55 is carried out asfollows. At S430, it is checked whether or not the value Cs of thespecified time point setting counter is zero. This processing is fordetermining whether or not the specified time point has occurred. Whenit is determined that the value of the specified time point settingcounter has been zeroed, processing is carried out to switch on any ofthe switching elements SW1 to SW6. More specifically, when thezero-crossing time point with which the value Cm of the counter is setas the value of the specified time point setting counter is U-phasezero-crossing time point (S432: YES), the following processing iscarried out. When the zero-crossing detection signal rises (S434: YES),the switching element SW1 is turned on (S436). When the zero-crossingdetection signal falls (S434: NO), the switching element SW2 is turnedon (S438).

Meanwhile, when the above zero-crossing time point is V-phasezero-crossing time point (S440: YES), the following processing iscarried out. When the zero-crossing detection signal rises (S442: YES),the switching element SW3 is turned on (S444). When the zero-crossingdetection signal falls (S442: NO), the switching element SW4 is turnedon (S446). When the above zero-crossing time point is W-phasezero-crossing time point (S440: NO), the following processing is carriedout. When the zero-crossing detection signal rises (S448: YES), theswitching element SW5 is turned on (S450). When the zero-crossingdetection signal falls (S448: NO), the switching element SW6 is turnedon (S452).

The technique for turning off the switching elements SW1 to SW6 issimilar to the foregoing. That is, they are turned off at a time pointdelayed by a predetermined electrical angle (e.g., 30°) from a specificspecified time point as illustrated in FIG. 53. More specifically, theswitching elements SW1, SW3, SW5 of the high side arms are turned off atthe time point delayed by a predetermined electrical angle fromzero-crossing time point in the rising process of an induced voltage ofa different phase. The switching elements SW2, SW4, SW6 of the low sidearms are turned off at the time point delayed by a predeterminedelectrical angle from zero-crossing time point in the falling process.This processing can also be carried out similarly to the processing inFIG. 55, and the description of it will be omitted.

As illustrated in FIGS. 56A and 56B as an example in acceleration, thezero-crossing time point depends on the rotational speed of thebrushless motor 2. For this reason, a problem arises when the rotationalspeed of the brushless motor 2 fluctuates. The rotational speed in atime interval between an occurrence of zero-crossing time point at thetime of initialization and the next occurrence of zero-crossing timepoint cannot be accurately represented by the value of the counterimmediately before initialization. For this reason, there is apossibility that the time point at which the value Cs of the specifiedtime point setting counter is zeroed is deviated from specified timepoint.

As an example of a case where rotational speed fluctuates, FIGS. 57 Aand 57B illustrate the result of an experiment on a setting error in thespecified time point in acceleration. When the initial speed of zero wasincreased to a predetermined speed as illustrated in FIG. 57A, adetection error (phase shifting) in the angle of the rotor was observedas illustrated in FIG. 57B. As understood from FIG. 57B, the phase shiftis especially large in the low speed range.

In this embodiment, consequently, information pertaining to change inthe rotational speed of the brushless motor 2 is extracted from theresult of detection of the zero-crossing time point, and the specifiedtime point is set based the extracted information. More specifically, achange in rotational speed contained in the above information isassociated with a period before an occurrence of the specified timepoint. However, it is presumed that the change in rotational speed canbe used to determine the difference between a rotational speed in thetime interval between adjacent occurrences of zero-crossing time pointimmediately before an occurrence of specified time point and arotational speed immediately before the occurrence of specified timepoint. Consequently, the above difference is determined based on theabove information and a specified time point is set.

FIG. 58A illustrates processing for setting a specified time point inthis embodiment. This processing is repeatedly carried out by the drivecontrol circuit 220, for example, in a predetermined cycle.

This series of processing is carried out as follows. At S460, it ischecked whether or not it is the time to cancel masking. That is, it ischecked whether or not the value Cmk of the masking period counter hasbeen zeroed. When it is the time to cancel masking, the value Cac of anacceleration detection counter is incremented at S462. At S464, it ischecked whether or not any of the comparison signals Uc, Vc, Wc has beeninverted as at S412 in FIG. 54. When an affirmative determination ismade at S464, it is determined at S466 whether or not the value Cac ofthe acceleration detection counter is equal to or higher than apredetermined value B. This processing is for determining whether or notthe brushless motor 2 is in an acceleration state. In this example, whenthe masking period is a period from an occurrence of the zero-crossingtime point to 45° and the increment speed of the acceleration detectioncounter is identical with the increment speed of the measuring counter,the following can be implemented. When the value of the accelerationdetection counter is smaller than ¼ times the previous value of thecounter, it can be determined that the brushless motor 2 is in anacceleration state. In this case, for this reason, the predeterminedvalue B is set to a value smaller than ¼ times the previous value of thecounter.

When it is determined at S466 that the brushless motor 2 is in anacceleration state, a correction amount ΔAi for correcting the value ofthe specified time point setting counter is set according to the valueof the acceleration detection counter at S468. Acceleration is increasedwith decrease in the value of the acceleration detection counter. Inconsideration thereof, in this example, the correction amount ΔAi is setto a larger value as the value Cac of the acceleration detection counteris decreased as illustrated in FIG. 58B. At S470, subsequently, a valueobtained by subtracting the correction amount ΔAi from the value Cs ofthe specified time point setting counter is set as a value Cs of thespecified time point setting counter.

When a negative determination is made at S466 or when the processing ofS470 is completed, the acceleration detection counter is initialized(Cac=0) at S472. When a negative determination is made at S460 or S464or when the processing of S472 is completed, this series of processingis once terminated.

FIG. 59 illustrates the mode for controlling the output of the brushlessmotor 2 in this embodiment. Specifically, (a) illustrates the transitionof the angle of the rotor; (b) illustrates the transition of rotationalspeed; and (c) illustrates the transition of phase current. It is to beunderstood that a detection error in specified time point is small inacceleration (for example, period 0.04 to 0.06 seconds) as well.Therefore, the rotational speed can be smoothly increased to a desiredrotational speed. If the correction processing for the measuringcounter, illustrated in FIG. 58A, is not carried out, meanwhile, theerror in the specified time point is large as illustrated in FIG. 60.Thus, the rotational speed cannot be smoothly increased.

According to the fifteenth embodiment, the following advantages can beprovided.

(1) Information pertaining to change in the rotational speed of thebrushless motor 2 is extracted from the result of detection ofzero-crossing time point, and a specified time point is set based onthis information. For this reason, a time required (value Cs of thespecified time point setting counter) from a specific occurrence ofzero-crossing time point to an occurrence of specified time point can becalculated with accuracy. Consequently, a specified time point can beset with accuracy.

(2) A time required (initial value of the specified time point settingcounter) from the occurrence of zero-crossing time point immediatelybefore an occurrence of specified time point to the occurrence ofspecified time point is calculated from the following interval: aninterval between occurrences of zero-crossing time point (the value ofthe counter). Further, it is corrected based on the above information.Thus, a time required (the initial value of the specified time pointsetting counter) can be calculated with accuracy even when therotational speed fluctuates.

(3) The above information is acquired based on a time from when maskingis canceled to when a zero-crossing time point occurs. Thus, the aboveinformation can be appropriately acquired.

(4) A specified time point is advanced more as the time untilzero-crossing time point occurs becomes shorter. Thus, the specifiedtime point can be set with accuracy according to acceleration.

Sixteenth Embodiment

In a sixteenth embodiment, the acceleration of the brushless motor 2 iscalculated from a result of detection of a zero-crossing time point, anda specified time point is variably set according to this acceleration.FIG. 61A illustrates processing for setting a specified time point inthis embodiment. This processing is repeatedly carried out by the drivecontrol circuit 220, for example, in a predetermined cycle.

This series of processing is carried out as follows. At S480 and S482,the processing of S410 and S412 in FIG. 54 is carried out to determinewhether or not it is zero-crossing time point. When it is zero-crossingtime point, processing of calculating acceleration Ai is carried out atS484. At this time, the acceleration Ai is calculated by the followingdifference: a difference between the reciprocal N(i) of the timeinterval between the previous occurrence of zero-crossing time point andthe present occurrence of zero-crossing time point and the reciprocalN(i−1) between the second previous occurrence of zero-crossing timepoint and the previous occurrence of zero-crossing time point. Inreality, this processing can be carried out by subtracting thereciprocal of the previous maximum value of the measuring counter fromthe reciprocal of the present maximum value of the measuring counter.Specifically, the acceleration ΔAi may be calculated as follows, with Tibeing defined as a previous zero-crossing time point.Ai=N(i)−N(i−1),N(i)=1/{Ti−T(i−1)}

At S486, subsequently, a correction amount ΔAi for correcting the valueCs of the specified time point setting counter is calculated accordingto the calculated acceleration Ai. At this time, the correction amountΔAi is determined as illustrated in FIG. 61B. That is, when theacceleration Ai is equal to or larger than a predetermined value A2(>0), the correction amount ΔAi is set to a negative value so that itsabsolute value is increased with increase in the acceleration Ai. Whenthe acceleration Ai is equal to or smaller than a predetermined value A1(<0), the correction amount ΔAi is set to a positive value so that itsabsolute value is increased with decrease in the acceleration Ai.

At S488, subsequently, the value Cs of the specified time point settingcounter is corrected by adding the correction amount ΔAi to the value Csof the specified time point setting counter. When a negativedetermination is made at S480 or S482 or when the processing of S488 iscompleted, this series of processing is once terminated.

According to the sixteenth embodiment, the following advantage can beprovided in addition to the advantages (1) and (2) of the fifteenthembodiment.

(5) The acceleration Ai of the brushless motor 2 is calculated based onmultiple values with respect to time intervals between occurrences ofzero-crossing time point, and a specified time point is set based onthis acceleration. Thus, a specified time point can be set with accuracyregardless of fluctuation in rotational speed.

Seventeenth Embodiment

When a zero-crossing time point occurs before the value Cmk of themasking period counter is zeroed, it is impossible to appropriately seta specified time point and to appropriately set the masking periodcounter and the like. To cope with this, this seventeenth embodiment isso constructed that a time Te that has elapsed from the occurrence ofzero-crossing time point to the present time is estimated based on aninduced voltage at that time. FIG. 62 illustrates processing in theabove estimation. This processing is repeatedly carried out by the drivecontrol circuit 220, for example, in a predetermined cycle.

This series of processing is carried out as follows. At S490, it ischecked whether or not it is the time to cancel masking, when the valueCmk of the masking period counter is changed to zero. When it is thetime to cancel masking, it is determined at S492 whether or not anoccurrence of zero-crossing time point has been completed. Thisprocessing can be carried out by taking the following measure. When aninduced voltage is in its rising process, it is checked whether or not aterminal voltage has already exceeded the reference voltage Vref. Whenthe induced voltage is in its falling process, it is checked whether ornot the terminal voltage has already fallen below the reference voltageVref.

When it is determined that an occurrence of zero-crossing time point hasbeen already completed, the processing proceeds to S494. At S494, a timeTe that has lapsed from the occurrence of zero-crossing time point tothe present time is estimated based on the previous value of the counterand the terminal voltage. When the masking is canceled, the terminalvoltage indicates the induced voltage. The difference between the valueof induced voltage and the reference voltage Vref contains informationpertaining to the above elapsed time Te. Since the amplitude of inducedvoltage depends on rotational speed, however, it is impossible toaccurately determine the elapsed time only by the present inducedvoltage. In this embodiment, consequently, the elapsed time is estimatedbased on the previous maximum value of the counter as a parameter havingcorrelation with rotational speed and the present induced voltage. Atthis time, for example, the following measure can be taken. Theswitching controller 227 is constructed of a microcomputer, and a datamap that defines the relation between the previous maximum value of thecounter and the present induced voltage and the elapsed time is used toestimate the elapsed time.

At S496, a value obtained by subtracting the elapsed time from thepresent value of the counter is set as the values Cs and Cmk of thespecified time point setting counter and the masking period counter.This processing is for setting a specified time point and a maskingperiod based on estimated zero-crossing time point. At S498, the valueCm of the counter is set to the elapsed time. When an affirmativedetermination is made at S490 or S492 or when the processing of S498 iscompleted, this series of processing is once terminated.

In the seventeenth embodiment, a time that has lapsed from theoccurrence of zero-crossing time point immediately before to the presenttime is estimated based on an induced voltage and a rotational speed.However, for example, a lapsed time may be estimated based on themaximum value or minimum value of induced voltage in the previousmasking canceled period and the present induced voltage. Morespecifically, a rotational speed is used in consideration of that theamplitude of induced voltage depends on rotational speed. The amplitudecan also be determined using the previous maximum value or minimum valueof the induced voltage instead.

According to this embodiment, the following advantages can be providedin addition to the advantages (1) to (4) of the fifteenth embodiment.

(6) When the occurrence of zero-crossing time point immediately beforehas already been completed when masking is canceled, a time that haselapsed from the occurrence of zero-crossing time point immediatelybefore to the present time is estimated based on an induced voltage.Thus, a time required from the occurrence of zero-crossing time pointimmediately before to an occurrence of specified time point can beestimated.

Eighteenth Embodiment

In this eighteenth embodiment, a limit value for the currents passedthrough the switching elements SW1 to SW6 is variably set according tothe acceleration of the brushless motor 2. FIG. 63 illustratesprocessing for setting the above current limit value. This processing isrepeatedly carried out by the drive control circuit 220, for example, ina predetermined cycle.

This series of processing is carried out as follows. At S500, theacceleration Ai is calculated. This processing is the same as theprocessing of S484 in FIG. 61. At S502, subsequently, it is checkedwhether or not the acceleration Ai is equal to or higher than a firstspecified acceleration Amax. The first specified acceleration Amax isset according to too high an acceleration at which degradation in theaccuracy of setting of the specified time point based on a time intervalbetween occurrences of zero-crossing time point becomes pronounced. Whenit is determined that the acceleration Ai is equal to or higher than thefirst specified acceleration Amax, the current limit value Li is reducedby ΔL1 (>0) at S504. This processing is for reducing the acceleration ofthe brushless motor 2.

When it is determined that the acceleration Ai is lower than the firstspecified acceleration Amax, it is determined at S506 whether or not itis equal to or lower than a second specified acceleration Amin. Thesecond specified acceleration Amin is set according to too low anacceleration (too high deceleration) at which degradation in theaccuracy of setting of specified time point based on a time intervalbetween occurrences of zero-crossing time point becomes pronounced. Whenit is determined that the acceleration is equal to or lower than thesecond specified acceleration Amin, the current limit value Li isincreased by ΔL2 (>0) at S508. This processing is for reducing theabsolute value of the acceleration of the brushless motor 2.

In this embodiment, the following processing is carried out in asituation in which the absolute value of acceleration Ai is excessivelylarge and thus the accuracy of setting of specified time point ispronouncedly degraded. Processing for reducing the absolute value ofacceleration is carried out. The accuracy of setting of specified timepoint is thereby enhanced. This setting is especially effective in thefollowing cases: cases where energization is basically carried by a120°-energization method to simply control rotational speed as in thisembodiment. More specifically, acceleration is determined by a loadapplied to the output shaft of the brushless motor 2 and the like, andit fluctuates from situation to situation. For example, when theviscosity of fuel in a fuel pump is low, the load applied to the outputshaft of the brushless motor 2 is light. Therefore, there is apossibility that acceleration becomes too high at the time of startup orthe like. When a measure is taken to prevent acceleration from becomingtoo high in a situation in which the viscosity of fuel is low, thefollowing takes place. In a situation in which the viscosity of fuel ishigh, a starting time is lengthened. Since there is a demand that astarting time should be shortened or for other like reasons, it isdifficult to prevent acceleration from becoming too high.

When the current supplied to the switching elements SW1 to SW6 exceeds acurrent limit value, PWM control is carried out instead of turning onthe switching elements SW1 to SW6 for a period of 120°. At this time,the state of the switching elements SW1 to SW6 is switched between theON state and the OFF state in a period of 120° from a specified timepoint. At this time, the time point with which the switching elementsSW1 to SW6 are brought into the ON state for the first time or the timepoint with which they are brought into the OFF state for the last timedoes not always agree with specified time point.

When the switching elements SW1 to SW6 are turned on and off by PWMcontrol, a current is supplied through the diodes D1 to D6. As a result,a period for which the terminal voltages Vu, Vv, Vw and the referencevoltage Vref disagree with each other is newly produced. Therefore, amasking period is additionally set.

In this embodiment, the current limit value maybe changed only whenacceleration is positive and too high.

According to this eighteenth embodiment, the following advantages can beprovided in addition to the advantages (1) to (4) of the fifteenthembodiment.

(7) A current limit value Li is variably set according to acceleration.Thus, increase in the absolute value of acceleration can be suppressedto the extent that the accuracy of time required computation based on atime interval between occurrences of zero-crossing time point is notexcessively degraded. For this reason, a specified time point can bemore accurately set by use of together information pertaining to changein rotational speed.

Nineteenth Embodiment

The induced voltage of the brushless motor 2 is produced in conjunctionwith rotation of the brushless motor 2. For this reason, when thebrushless motor 2 at a stop is started, switching operation based on theinduced voltage cannot be performed. To cope with this, the measureillustrated in FIG. 64A is normally taken when the brushless motor 2 isstarted. The angle (electrical angle) of the rotor is fixed by passing acurrent from a specific phase to another specific phase, that is,positioning processing is carried out. In the example illustrated inFIG. 55, the switching element SW1 of the high side arm and theswitching element SW6 of the low side arm are brought into the ON state,and a current is thereby passed from the U-phase to the W-phase to fixthe angle of the rotor of the brushless motor 2. When the angle of therotor is fixed by this processing, a long time may be required for theangle of the rotor to settle. For this reason, there is a possibilitythat a starting time of the brushless motor 2 is lengthened.

In a nineteenth embodiment, processing illustrated in FIG. 64B iscarried out. That is, a switching element of one phase of the high sidearms of the brushless motor 2 and switching elements of two phases ofthe low side arms are brought into the ON state to pass a current fromone phase to two phases (one-phase/two-phase energization). The angle ofthe rotor of the brushless motor 2 is thereby fixed at a predeterminedangle. FIG. 64B illustrates an example of cases where the followingprocessing is carried out. The switching element SW1 of the high sidearm and the switching elements SW4, SW6 of the low side arms are broughtinto the ON state, and the current is thereby passed from the U-phase tothe V-phase and the W-phase. Thus, such force as to reduce the deviationof the angle of the rotor of the brushless motor 2 from a predeterminedangle is exerted; therefore, a time it takes for the angle of the rotorto settle to the predetermined angle can be shortened.

FIG. 65A illustrates the way the angle of the rotor is settled by thepositioning processing illustrated in FIG. 64A, and FIG. 65B illustratesthe way the angle of the rotor is settled by the positioning processingillustrated in FIG. 64B. In these figures, Iu, Iv, Iw indicate phasecurrents, and Im and Ip indicate a motor phase current and a powersource current, respectively. According to the positioning processing inthis embodiment, as illustrated in FIG. 65B, the time it takes for theangle of the rotor to settle is short, and fluctuation in the currentshaving correlation with fluctuation in the angle of the rotor ceasesearly.

Setting a predetermined angle may be carried out as illustrated in FIG.66, which illustrates the relation between the predetermined angle andthe starting time. In this example, an angle of 0° is defined as anangle to which the rotation angle is assumed to settle if the initialstate of switching operation is continued when the brushless motor 2 isstarted. This figure illustrates starting time (period) with respect toa case where a current supplied to the brushless motor 2 is not limitedin the positioning processing and with respect to a case where thecurrent is limited.

When the predetermined angle is set within a range from ahead of anangle delayed by 150° to behind an angle advanced by 30°, the motor canbe favorably started. This relates to that there is the relationillustrated in FIG. 67 between torque generated when the switchingoperation is started in conjunction with startup of the brushless motor2 and the predetermined angle. In this example, torque having a positivevalue refers to torque that rotates the brushless motor 2 in thepositive direction. In the range on the advanced side, torque thatrotates in reverse the brushless motor 2 is produced. Therefore, thebrushless motor 2 is prone to be reversely rotated. The output torque ismaximized at an angle delayed by 60°. For this reason, the following canbe implemented in proximity to an angle delayed by 60°. As illustratedin FIG. 66, the starting time can be especially shortened regardless ofwhether or not the current supplied to the brushless motor 2 is limitedin positioning processing. In this embodiment, consequently, thepredetermined angle is set in proximity to the angle delayed by 60°.

FIG. 68 illustrates processing for starting the brushless motor 2 inthis embodiment. This processing is triggered by an ignition switchbeing turned on (IG-ON) and carried out by the drive control circuit220.

When the ignition switch is turned on, positioning processing by theone-phase/two-phase energization is carried out at S510. At S512, it ischecked whether or not a predetermined time Tdi has lapsed after thestart of positioning processing. The predetermined time Tdi is set to atime that is equal to or longer than a time in which the angle of therotor is assumed to settle to the predetermined angle byone-phase/two-phase energization and is as short as possible. When thepredetermined time Tdi has elapsed, the positioning processing isterminated at S514. That is, the ON operation for the one phase of thehigh side arm and the two phases of the low side arms is stopped, andthese phases are changed to the OFF operation state. At S516, thebrushless motor 2 is started. The processing of S514 may be carried outas the processing of changing the state of switching operation for theabove one-phase/two-phase energization to the initial state of switchingoperation in conjunction with startup of the brushless motor 2. When theprocessing of S516 is completed, this series of processing is onceterminated.

According to the nineteenth embodiment, the following advantages can beprovided in addition to the advantages (1) to (4) of the fifteenthembodiment.

(8) Prior to a startup of the brushless motor 2, a current is suppliedfrom one phase to two other phases of the brushless motor 2 to fix theangle of the rotor of the brushless motor 2 at a predetermined angle.Thus, a time it takes for the angle to settle to the predetermined anglecan be shortened, and thus the starting time of the brushless motor 2can be shortened.

(9) The predetermined angle is set in proximity to an angle delayed by60° from the settled value of the rotor of the brushless motor 2 assumedif the initial state of switching operation in conjunction with thestartup of the brushless motor 2 is continued. Thus, large rotary torquein the positive direction can be generated by the first switchingoperation, and consequently, the starting time can be shortened.

Twentieth Embodiment

When the above positioning processing by the one-phase/two-phaseenergization is carried out, rotary torque may not be generated by theone-phase/two-phase energization depending on the stop position of thebrushless motor 2 before the positioning processing is started. Morespecifically, as apparent from FIG. 67, the rotary torque is notgenerated when the predetermined angle and the stop position are shiftedfrom each other by 180°. In this case, consequently, there is apossibility that positioning cannot be appropriately carried out by theabove processing.

In a twentieth embodiment, consequently, positioning processing isachieved by carrying out one-phase/two-phase energization twice. FIG. 69illustrates processing for starting the brushless motor 2 in thisembodiment. This processing is triggered by the ignition switch beingturned on and carried out by the drive control circuit 220.

This series of processing is carried out as follows. At S520, tentativepositioning processing by one-phase/two-phase energization is carriedout. At this time, the angle of the rotor is fixed at an angle differentfrom a predetermined angle. When a predetermined time Tdi has elapsed(S522: YES), the tentative positioning processing is terminated at S524.At S526, subsequently, final positioning processing is carried out bythe one-phase/two-phase energization. That is, this positioningprocessing is carried out to settle the angle of the rotor to thepredetermined angle. At this time, the predetermined angle is set as inthe fifteenth embodiment. That is, it is set to the angle in proximityto an angle delayed by 60° from the settled value of the angle of therotor obtained if the initial state of switching operation inconjunction with startup of the brushless motor 2 is continued. Thepredetermined angle is so set that the angular difference between theangle at which the rotor is fixed by the above tentative positioningprocessing and the angle at which the rotor is fixed by the finalpositioning processing is larger than 0° and smaller than 180°. It ismore desirably set so that the angular difference is substantially 60.When the time of the final positioning processing becomes equal to thepredetermined time Tdi, the final positioning processing is terminatedat S530. At S532, the brushless motor 2 is started.

According to the above processing, the following can be implemented evenwhen the difference between the angle of the rotor of the brushlessmotor 2 and the predetermined angle is 180°. The brushless motor 2 canbe rotated by tentative positioning processing to control the differencefrom the predetermined angle to less than 180°. For this reason, theangle of the rotor of the brushless motor 2 can be fixed at thepredetermined angle without fail by final positioning processing. Whenthe angle of the rotor of the brushless motor 2 prior to positioningprocessing is such an angle that the rotary torque is not generated bytentative positioning processing, this angle is an angle at which therotary torque is generated by the final positioning processing. For thisreason, the rotor can be rotated to the predetermined angle by the finalpositioning processing.

The following can be implemented by making the difference between theangle at which the rotor is fixed by the tentative positioningprocessing and the predetermined angle close to 60°. The predeterminedtime Tdi at S528 can be made shorter than the predetermined time Tdi atS512 in FIG. 68. The reason for this is as follows. The rotary torquegenerated in the brushless motor 2 when the final positioning processingis started is increased. As a result, a time required for the angle atwhich the rotor is fixed by the tentative positioning processing totransition to the predetermined angle is shortened.

According to the twentieth embodiment, the following advantage can beprovided in addition to the advantages (8) and (9) of the nineteenthembodiment.

(10) The angle of the rotor of the brushless motor 2 is fixed at apredetermined angle by carrying out the one-phase/two-phase energizationtwice with the fixed position varied. Thus, the angle of the rotor canbe fixed at the predetermined angle without fail regardless of the angleof the rotor of the brushless motor 2 prior to the positioningprocessing.

Twenty-first Embodiment

In a twenty-first embodiment, as illustrated in FIG. 70, processing forstarting a brushless motor 2 is triggered by the ignition switch beingturned on and is carried out by the drive control circuit 220. Thisseries of processing is similar to but different from the nineteenthembodiment (FIG. 68) in S540 and S542.

When it is determined at S512 that the predetermined time Tdis haselapsed, all-phase short-circuiting processing is carried out at S540.In this processing, the switching elements SW1, SW3, SW5 of the highside arms or the switching elements SW2, SW4, SW6 of the low side armsare all turned on. When the all-phase short-circuiting processing iscarried out for a predetermined time Ts (S542: YES), the brushless motor2 is started.

According to the all-phase short-circuiting processing, a current issupplied through the brushless motor 2 by the induced voltage inconjunction with rotation of the brushless motor 2. This current isattenuated by the resistance of the current passage and the like. Inother words, rotational energy is attenuated. For this reason, thebrushless motor 2 can be quickly stopped at the predetermined angle. Thepredetermined time Ts is set to a time that meets the followingconditions: the time should be equal to or longer than a time in whichvibration is attenuated by the all-phase short-circuiting processing sothat the angle of the rotor of the brushless motor 2 settles to thepredetermined angle and the motor is substantially stopped; and the timeshould be as short as possible.

According to this processing, it is unnecessary to determine thepredetermined time Tdis at S512 according to a time it takes for theangle of the rotor of the brushless motor 2 to settle to thepredetermined angle. The predetermined time can be determined accordingto a time required to cause the angle of the rotor to transition to apredetermined angle. For this reason, the predetermined time Tdis can bemade shorter than the predetermined time Tdi at S512 in FIG. 68.

According to the twenty-first embodiment, the following advantage can beprovided in addition to the advantages (8) and (9) of the nineteenthembodiment.

(11) After the processing by one-phase/two-phase energization, all thephases of the brushless motor 2 are short-circuited. Thus, a time ittakes for the angle of the rotor to settle to the predetermined anglecan be further shortened.

Twenty-second Embodiment

FIG. 71 illustrates processing for starting the brushless motor 2 in atwenty-second embodiment. This processing is triggered by the ignitionswitch being turned on and is carried out by the drive control circuit220. This processing is similar to but different from the processing ofthe twentieth embodiment (FIG. 69) in S544 and S546.

This series of processing is carried out as follows. All-phaseshort-circuiting processing is carried out (S544 and S546) when thefollowing processing is carried out. It is carried out when theone-phase/two-phase energization for the tentative positioningprocessing is carried out for the predetermined time Tdis (S522: YES).In addition, it is carried out when the one-phase/two-phase energizationfor the final positioning processing is carried out for thepredetermined time Tdis (S528: YES). Thus, the time required forpositioning can be shortened as compared with the twentieth embodiment(FIG. 69).

Twenty-third Embodiment

A twenty-third embodiment is a modification of the twentieth embodiment(FIG. 69).

When the current supplied to the switching elements SW1 to SW6 becomesequal to or larger than the predetermined value in the 120°-energizationcontrol, PWM control is carried out to limit it. In this embodiment, PWMcontrol is also carried out when the current supplied to the switchingelements SW1 to SW6 is equal to or larger than a predetermined value inthe positioning processing.

FIG. 72 illustrates processing in current limit control in thistwenty-third embodiment. This processing is repeatedly carried out bythe drive control circuit 220, for example, in a predetermined cycle.

At S550, it is checked whether or not the positioning processing isunderway. When it is determined that the positioning processing isunderway, it is determined at S552 whether or not the amount of currentIh of the switching elements SW1, SW3, SW5 of the high side arms isequal to or larger than a threshold current Ith. This processing is fordetermining whether or not the amount of current Ih is too large duringthe positioning processing. When it is determined that the amount ofcurrent Ihs is equal to or larger than the threshold current Ith, allthe switching elements SW2, SW4, SW6 of the low side arms are turned offat S554. When a negative determination is made at S550 or S552 or whenthe processing of S554 is completed, this series of processing is onceterminated.

In this twenty-third embodiment, the current may be limited by turningoff the switching elements of the high side arms. In this case, however,processing is carried out to limit the current according to, forexample, whether or not the sum of the values of currents passed throughthe switching elements of the low side arms is equal to or larger than apredetermined value.

According to the twenty-third embodiment, the following advantage (12)can be provided in addition to the advantages (8) and (9).

(12) When the amount of current supplied to the brushless motor 2becomes equal to or larger than the predetermined value due to theone-phase/two-phase energization in positioning processing, the amountof energization is limited. Thus, the power consumption in positioningprocessing can be prevented from becoming excessively large. Inaddition, it is possible to prevent torque produced by energizingoperation for positioning from becoming too high and shorten a time ittakes for the rotation angle to settle.

Twenty-fourth Embodiment

FIG. 73 illustrates processing associated with start of processing forstarting the brushless motor 2 in a twenty-fourth embodiment. Thisprocessing is triggered by the ignition switch being turned on and isrepeatedly carried out by the drive control circuit 220, for example, ina predetermined cycle.

In this processing, when a period for which the voltage VB of thebattery 214 is equal to or higher than a specified voltage Vth lasts fora predetermined time Tv or longer (S560: YES), the following processingis carried out. Various parameters for controlling the brushless motor 2in the drive control circuit 220 are initialized (S562), and processingassociated with startup of the brushless motor 2 is carried out (S564).That is, the processing illustrated in FIG. 68 is carried out.

The specified voltage Vth is set to a value obtained by adding apredetermined margin to a voltage required for the operation of thedrive control circuit 220 to stabilize. When the startup of thebrushless motor 2 is restrained until a state in which the voltage ofthe battery 214 is equal to or higher than the specified voltage Vthlasts for the predetermined time TV or longer, the following can beimplemented. As illustrated in FIG. 74, the brushless motor 2 can bestarted when the voltage of the battery 214 has been stabilized.

The reason why the initialization of S562 is carried out is as follows.Since the voltage applied to the drive control circuit 220 drops once,there is a possibility that the reliability of the parameters used inthe drive control circuit 220 is degraded.

According to the twenty-fourth embodiment, the following advantages canbe provided in addition to the advantages (8) and (9) of the twentiethembodiment.

(13) The brushless motor 2 is restrained from being started until thevoltage of the brushless motor 2 becomes equal to or higher than apredetermined specified voltage. Thus, it is possible to prevent anevent that the operation of the drive control circuit 220 isdestabilized and the rotating state of the brushless motor 2 gets out ofcontrol and the like. For this reason, a situation in which the rotationof the brushless motor 2 is stopped and then starting processing iscarried out again can be avoided.

(14) The brushless motor 2 is restrained from being started until aperiod for which the voltage of the battery 214 is equal to or higherthan a specified voltage lasts for a predetermined time Tv. Thus, themotor can be started with the voltage of the battery 214 stabilized.

The fifteenth to twenty-fourth embodiments may be modified as describedbelow.

The modification to the nineteenth embodiment made in the twenty-thirdembodiment may be applied to the twenty-first to twenty-secondembodiments. The modification to the nineteenth embodiment made in thetwenty-fourth embodiment may be applied to the fifteenth to thenineteenth and twenty-second to twenty-third embodiments.

The positioning processing need not be carried out by turning on theswitching element of one phase of the high side arm and switchingelements of the two other phases of the low side arms to pass a currentfrom the one phase to the two other phases. For example, it may becarried out by turning on the switching elements of two phases of thehigh side arms and the switching element of the one other phase of thelow side arm to pass a current from the two phases to the one phase. Ifthe brushless motor 2 of four or more phases is used, for example,positioning processing may be carried out as follows. Switching elementsof two phases of the high side arms are turned on and further, switchingelements of two phases of the low side arms are turned on.

The predetermined angle is not limited to those described as an examplewith respect to the above embodiments. In this case, it is desirable toset the predetermined angle within an angle domain from ahead of anangle delayed by 180° to behind an angle advanced by 30°. To generatepositive torque by the initial switching operation to start thebrushless motor 2, it is desirable to set the predetermined angle on thedelayed side. In addition, from the viewpoint of reducing a startingtime regardless of whether or not a current is limited, it is desirableto set the predetermined angle ahead of an angle delayed by 120°.

The technique for setting a specified time point need not be thefollowing method: a time required from the occurrence of zero-crossingtime point immediately before to an occurrence of specified time pointis calculated according to a time interval between occurrences ofzero-crossing time point; and the calculated time required is correctedaccording to change in rotational speed. For example, a two-dimensionalmap defining the relation between rotational speed, acceleration, andtime required may be used. Further, a time required t may be calculatedfrom a predetermined angle during a period from an occurrence ofzero-crossing time point to an occurrence of specified time point,rotational speed Ni, and acceleration Ai, by an expression ofpredetermined angle=Ni×t+(1/2)×Ai×t×t.

The technique for extracting information pertaining to change in arotational speed from a result of detection of a zero-crossing timepoint and setting a specified time point based on this information isnot limited to those described with respect to the above embodiments orthe modifications thereto. For example, a value obtained by thefollowing expression may be taken as the value of the specified timepoint setting counter at an occurrence of zero-crossing time point:present value of the counter×(present value of the counter/previousvalue of the counter). A value obtained by present value of thecounter−K×(present value of the counter−previous value of the counter)may be taken as the value of the specified time point setting counter.That is, any technique can be used as long as the above information isextracted by use of three or more results of zero-crossing time pointdetection and a specified time point is set based on this information.

The construction of the current detector 228 is not limited to thosedescribed as an example with respect to the above-embodiments. Forexample, it may be so constructed that a shunt resistor is providedbetween each switching element SW1, SW3, SW5 and the positive potentialof the battery 214 and a current supplied to them is detected based onthe amount of voltage drop by the shunt resistor.

The brushless motor 2 need not be an actuator mounted in a fuel pump andmay be, for example, an actuator of a fan for cooling a radiator of anin-vehicle internal combustion engine. Further, it may be a motorprovided in a data recorder or a reproducer mounted in an automobilenavigation system or the like. That is, it may be a motor provided in adata recorder or a reproducer for disc media, such as DVD (DigitalVersatile Disc), CD-ROM (Compact Disc Read Only Memory), and hard disc.The rotary machine need not be a motor and may be a generator.

The power supply need not be a battery 214 and may be a generatorconfigured to convert the rotational energy of an in-vehicle internalcombustion engine into electrical energy.

1. A rotary machine driving apparatus for a rotary machine comprising: asensorless mode driving means that drives the rotary machine in asensorless mode after the rotary machine is driven to an initialposition and started to rotate by forced commutation of currentssupplied to the rotary machine; a loss-of-synchronism predicting meansthat monitors, while the rotary machine is driven in the sensorless modeby the sensorless mode driving means, a state of rotation of the rotarymachine and thereby detects a sign of the rotary machine transitioningto a state of loss of synchronism; and a drive controlling means that,when the sign is detected by the loss-of-synchronism predicting means,temporarily stops driving of the rotary machine to bring the rotarymachine into a free running state and thereafter carries out control soas to resume driving of the rotary machine.
 2. The rotary machinedriving apparatus of claim 1, wherein: the loss-of-synchronismpredicting means detects a speed of the rotary machine, compares thedetected speed with a normal speed of the rotary machine, and detectsthe sign when a difference between the detected speed and the normalspeed becomes equal to or higher than a predetermined value.
 3. Therotary machine driving apparatus of claim 2, wherein: theloss-of-synchronism, predicting means detects a period equivalent to anelectrical angle of 60° based on the zero-crossing time point of aninduced voltage of the rotary machine and compares a length of thedetected period with a period equivalent to an electrical angle of 60°at a normal speed in case of the rotary machine being a three-phaserotary machine.
 4. The rotary machine driving apparatus of claim 1,wherein: the loss-of-synchronism predicting means detects the sign whena period, for which a pattern of development of the output voltage ofeach phase for the rotary machine disagrees with a predetermineddevelopmental pattern, becomes equal to or larger than a predeterminedvalue.
 5. The rotary machine driving apparatus of claim 1, wherein: theloss-of-synchronism predicting means discriminates an induced voltage ofthe rotary machine into three levels that are high level, low level andnon-energization level set between the high level and the low level, indetecting a pattern of development of the induced voltage of each phase.6. The rotary machine driving apparatus of claim 1, wherein: theloss-of-synchronism predicting means detects a current supplied to therotary machine, and detects the sign when fluctuation in the currentbecomes equal to or higher than a predetermined value.
 7. The rotarymachine driving method of claim 6, wherein: the monitoring detects apattern of development of an induced voltage of each phase of the rotarymachine, and discriminates the induced voltage into three levels thatare high level, low level and non-energization level set between thehigh level and the low level.
 8. The rotary machine driving method ofclaim 6, wherein: the monitoring detects a current supplied to therotary machine, and detects the sign when fluctuation in the currentbecomes equal to or higher than a predetermined value.
 9. A rotarymachine driving method comprising: detecting an induced voltagedeveloped in a winding of a rotary machine; estimating a rotor positionof the rotary machine based on the detected induced voltage thereby toobtain an energization time point for the rotary machine, characterizedby driving the rotary machine to start rotation by forced commutationafter driving to an initial position by currents supplied to the rotarymachine; driving the rotary machine in a sensorless mode by supplyingthe currents in a predetermined commutation pattern after the rotarymachine is started to rotate; monitoring a state of rotation of therotary machine and thereby detecting a sign of the rotary machinetransitioning to a state of loss of synchronism, while the rotarymachine is driven in the sensorless mode; and temporarily stoppingdriving of the rotary machine to bring the rotary machine into a freerunning state when the sign is detected, and thereafter carrying outcontrol so as to resume driving of the rotary machine.
 10. The rotarymachine driving method of claim 9, wherein: the monitoring detects thesign by either (1) comparing a detected speed of the rotary machine witha normal speed of the rotary machine, (2) comparing a length of adetected period equivalent to an electrical angle of 60° based on thezero-crossing time point of the induced voltage of the rotary machinewith a period equivalent to an electrical angle of 60° at the normalspeed, or (3) comparing a period for which a pattern of development ofoutput voltage of each phase for the rotary machine disagrees with apredetermined developmental pattern becomes equal to or larger than apredetermined value.
 11. A rotary machine driving apparatus for a rotarymachine comprising: a forced commutation means for carrying out forcedcommutation to start the rotary machine before driving the rotarymachine is a sensorless mode; and a torque limiting means for limiting acurrent supplied to a winding of the rotary machine to an upper limitlevel set higher than a level at which a current flows, when the rotarymachine is in a normal rotating state, when the forced commutation meanscarries out the forced commutation, wherein the torque limiting means isconfigured to detect a current supplied to the rotary machine, compare adetected current with a reference corresponding to the upper limitlevel, and turn off supply of the current to the rotary machine when acomparison result indicates that the detected current exceeds the upperlimit level.
 12. The rotary machine driving apparatus of claim 11,wherein: the forced commutation means starts the forced commutationafter positioning a rotor of the rotary machine; and the torque limitingmeans energizes the winding at a phase angle which is advanced by apredetermined amount from an appropriate phase angle relative to therotor position.
 13. A rotary machine driving method for a rotary machinecomprising: detecting an induced voltage developed in a winding of therotary machine when the rotary machine is driven in a sensorless mode;estimating a rotor position of the rotary machine based on the detectedinduced voltage thereby to obtain an energization time point for therotary machine; characterized by detecting a current supplied to therotary machine when the rotary machine is driven to start rotation byforced commutation of the current supplied before being driven in thesensorless mode; and limiting the current supplied to the winding of therotary machine to an upper limit level set higher than a level at whicha current flows in a steady rotating state of the rotary machine, whenthe current detected exceeds the upper limit level under a conditionthat the forced commutation is carried out to start the rotary machine.14. The rotary machine driving method of claim 13, further comprising:starting the forced commutation after the rotor is positioned at aninitial position; and energizing, simultaneously with the starting, thewinding of the rotary machine at a phase angle which is advanced by apredetermined amount from an appropriate phase angle relative to therotor position.
 15. The rotary machine driving method of claim 14,wherein: the predetermined amount is about 30° in electrical angle ofthe rotary machine.
 16. A rotary machine driving method comprising:comparing a terminal voltage of a rotary machine with a referencevoltage with respect to magnitude to detect a zero-crossing time pointwhen the reference voltage, which is either a neutral point voltage ofthe rotary machine or an equivalent thereof, and an induced voltage ofthe rotary machine agree with each other; operating switching elementsto control a supply of current to the rotary machine based on thezero-crossing time point; and offset-correcting at least one of a valueof the terminal voltage and a value of the reference voltage, which arecompared with each other by the comparing means, to differentiate thevalues of the terminal voltage and the reference voltage when arotational speed of the rotary machine is substantially zero, at whichtime the terminal voltage and the reference voltage are generally equal.17. The rotary machine driving method of claim 16, wherein: the rotarymachine is a multi-phase rotary machine, and the offset-correctingcarries out an offset correction so that a result of comparison madewhen the rotational speed of the multi-phase rotary machine issubstantially zero becomes the same for all phases.
 18. A rotary machinedriving apparatus for a rotary machine comprising: a loss-of-synchronismpredicting means that monitors a state of rotation of the rotary machineand thereby detects a sign of the rotary machine transitioning to astate of loss of synchronism; and a drive controlling means that, whenthe sign is detected by the loss-of-synchronism predicting means,temporarily stops driving the rotary machine to bring the rotary machineinto a free running state and thereafter carries out control to resumedriving of the rotary machine, wherein the loss-of-synchronismpredicting means detects a speed of the rotary machine, compares thedetected speed with a normal speed of the rotary machine, and detectsthe sign when a difference between the detected speed and the normalspeed becomes equal to or higher than a predetermined difference,wherein the loss-of-synchronism predicting means detects a periodequivalent to an electrical angle of 60° based on the zero-crossing timepoint of an induced voltage of the rotary machine and compares a lengthof the detected period with a period equivalent to an electrical angleof 60° at a normal speed if the rotary machine is a three-phase rotarymachine, and wherein the loss-of-synchronism predicting means detectsthe sign when a period, for which a pattern of development of the outputvoltage of each phase for the rotary machine disagrees with apredetermined development pattern, becomes equal to or larger than apredetermined period.
 19. A rotary machine driving apparatus comprising:a power conversion circuit including a switching element; a comparingmeans for comparing a terminal voltage of a rotary machine with areference voltage with respect to magnitude to detect a zero-crossingtime point when the reference voltage, which is either a neutral pointvoltage of the rotary machine or an equivalent thereof, and an inducedvoltage of the rotary machine agree with each other, and operating theswitching element to control a supply of current to the rotary machinebased on the zero-crossing time point; and a correcting means foroffset-correcting at least one of a value of the terminal voltage and avalue of the reference voltage, which are compared with each other bythe comparing means, so as to differentiate the values of the terminalvoltage and the reference voltage when a rotational speed of the rotarymachine is substantially zero, at which the terminal voltage and thereference voltage are generally equal to each other, wherein the rotarymachine is a multi-phase rotary machine, and the correcting meanscarries out an offset correction so that a result of comparison by thecomparing means when the rotational speed of the multi-phase rotarymachine is substantially zero becomes the same for all phases.